Popular Science Monthly/Volume 17/October 1880/Modern Aspects of the Life-Question
By Professor GEORGE F. BARKER.
The number of roots in our equation of life increases the difficulty of solving it, but by no means permits the acceptance of the lazy assumption that it is altogether insoluble or reduces a sagacious guess to the level of the prophecy of a quack.—Haughton.
THE discovery of new truth is the grand object of scientific work. The exultation of feeling which comes from the possession of a fact, which now, for the first time, he makes known to men, must ever be the reward of the scientific worker. As investigators and as students of science we are met here to-day at this our annual session. Each of us during the past year has been endeavoring to push outward further into the unknown, the boundary of present knowledge. When, therefore, we thus meet together, it is fitting that, from time to time, our attention should be called to the progress which has been made along some one of the various lines of research, and to the milestones which mark the epochs of advance along the way which science has traveled. Moreover, we may profitably sum up at such times the work done in particular directions, and encourage ourselves with prospective and retrospective glances. In these summings up, however, a difficulty arises. The range of modern scientific thought includes an immense area. The field of knowledge is already so vast that, seen from the vertical distance necessary to make a wide survey, that small portion of it which is familiar to any one individual is scarcely visible. In consequence, to use a mechanical figure, the solid contents of a man's acquirements being given, the depth thereof is inversely as the area covered. He, therefore, who undertakes to speak even for one single department of science distributes his stock of knowledge over so broad a surface that in places it must become dangerously thin. It is, therefore, with a very keen sense of the temerity involved in the undertaking that I ask your attention, during the hour allotted me, to some points which appear to me to have been recently gained in the discussion of the question of life.
My friend and predecessor, Professor Marsh, opened his excellent address at Saratoga with the question, "What is Life?" In a somewhat different sense I too ask the same question. But I fear it is only to echo his reply, "The answer is not yet." The result, however, can not long be doubtful. "A thousand earnest seekers after truth seem to be slowly approaching a solution." And, though the ignis fatuus of life still dances over the bogs of our misty knowledge, yet its true character can not finally elude our investigation. The progress already made has hemmed it in on every side; and the province within which exclusively vital acts are now performed narrows with each year of scientific research.
What now are we to understand by the word "Life" in this discussion? A noteworthy parallel is disclosed in the progress of human knowledge between the ideas of life and of force. Both conceptions have advanced, though not with equal rapidity, from a stage of complete separability from matter to one of complete inseparability. Life is now universally regarded as a phenomenon of matter, and hence, of course, as having no separate existence. But there still exists a certain vagueness in the meaning of the term "life." Two distinct senses of this word are in use; the one metaphysical, the other physiological. The former, synonymous with mind and soul, at least in the higher animals, has been evolved from human consciousness; the latter has arisen from a more or less careful investigation of the phenomena of living beings. It need scarcely be said that it is in the sense last mentioned that the word "life" is used in science. The conception represents simply the sum of the phenomena exhibited by a living being.
Moreover, the progress which has been made in the solution of the life-question has been gained chiefly by investigation of special functions. But the functions of a vital organism are themselves vital. What, then, is the meaning of "vital" as applied to a function? Fortunately, the answer is not difficult. "Life," says Küss, the distinguished Strasburg physiologist, "is all that can not be explained by chemistry or physics." Guided by such a definition the work of the physiological investigator is simple. He has only to test each separate operation which he finds going on in the organism, and to declare whether it be chemical or physical, If it be either, then, since each function is non-vital, the entire organism must be non-vital also. Hundreds of able investigators, provided with the most effective appliances of research, are now in full cry after the life-principle. Naturally, a vast amount of collateral knowledge is accumulated in the process. The quantitative as well as the qualitative relations of things are fixed and many important facts are collected.
With the object in view thus clearly defined, we are not surprised that great progress has been made. A vital process, like the catalytic ones of the older chemistry, was found by such research to be simply a process which, for want of sufficient investigation, is not yet understood. While therefore, undoubtedly, much work yet remains to be done in the realm still called vital, the prophetic vision is already bright which will witness the last traces of inexplicable phenomena vanish and the words expressing them relegated to the limbo of the obsolete.
As a first result of recent work, the living organism has been brought absolutely within the action of the law of the Conservation of Energy. Whether it be plant or animal, the whole of its energy must come from without itself, being either absorbed directly or stored up in the food. An animal, like a machine, only transforms its energy. Lavoisier's Guinea-pig placed in the calorimeter gave as accurate a heat-return for the energy it had absorbed in its food as any thermic engine would have done. But the parallel goes further. The mechanical work of an engine is measured by the loss of its heat and not of its substance. So the mechanical or intellectual work of a living being is measured by the amount of food rather than the amount of tissue which is burned. The energy evolved daily by the human body would raise it to a height of about six miles.
But, besides heat, work may be the outcome of the organism; and this through the agency of the muscles. Their absolute obedience to mechanical law in their mode of action has been admirably established by Haughton. The work a muscle does, it does in contracting. It is to the mechanism of muscle-contraction that we are indebted for another illustration of our subject.
When work is done by a muscle in contracting, three changes are observed to take place in its tissue: First, there is a loss of its electric tension; second, there is an evolution of heat in it; and, third, carbon dioxide appears there, and its reaction, before neutral, becomes acid.
Matteucci was the first to observe and to call attention to the remarkable similarity, in structure and in the mechanism of operation, between striated muscular fiber and the electric organ of certain fishes. Recently, Marey has repeated and extended his observations. In structure, the electric organ is made up, like the muscle, of columnar masses each separable transversely into vesicular sections. In a torpedo weighing seventy-three pounds, there were 1,182 of these columns, with 150 sections, on an average, in each. In the muscles which bend the forearm, there are 798,000 fibrillæ. As 'to the mechanism, alike in muscle and in electric organ, an electric current stimulates action on opening and on closing the circuit, but not when it is flowing; the same phenomena take place in both with the direct and with the inverse current; both are reflex; stimulation of the electric nerve produces discharge, as that of the motor nerve causes muscular shock; an entire paralysis follows nerve-section; curare paralyzes both; and tetanus results in both from rapid currents or from strychnine.
Still more striking analogies are furnished by the investigation of the susurrus or muscular sound, first noticed in 1809 by Wollaston. This sound is produced by all muscles when in the state of contraction, the pitch of the note being not far from thirty vibrations per second. It is evidently only the intermittent discharge of the muscular fiber. A single excitation produces a muscular shock. As this production requires from eight to ten hundredths of a second, it is evident that, if another stimulus be applied before the first has disappeared, the two will coalesce; and when twenty per second reach the muscle it becomes permanently contracted or tetanized. By means of a very sensitive myograph, Marey has found that in voluntary contraction the motor nerves are the seats of successive acts, each of which produces an excitation of the muscle. In 1877 Marey examined similarly the discharge of the torpedo, and found a most complete correspondence between it and muscular contraction. Since electric tension disappears from a muscle during contraction, is not the evidence conclusive that muscular contraction, like the discharge of the electric organ of the torpedo, is an electrical phenomenon?
Granting electric discharge to be the cause of muscle-contraction, what is its origin? That it is not carried to the muscle by the nerves follows from the fact that a muscle will still contract when deprived of all its nerve-fibers. It must therefore be generated within the muscle itself. To reach a solution of the problem we must obviously follow the analogies of its production elsewhere.
Perhaps no single question in physics has been more keenly discussed than this one of the origin of electric charge. The memorable conflict between Galvani and Volta, between animal electricity and the electricity of metallic contact, succeeded by the even more triumphant overthrow of the latter and the establishment ultimately by Faraday of the electro-chemical theory—these are facts fresh in all our memories. The justice of time, however, in this case, if it has been tardy, has been none the less sure. The experiments of Thomson have vindicated Volta and established the contact theory as a vera causa. And, more curiously still, it now appears to be proved that both contact and chemical action underlie the production of that very animal electricity so stoutly battled for by Galvani and his associates.
Volta's experiments to prove that a difference of potential is developed by the contact of two heterogeneous metals were not crucial. But Thomson, repeating them with the aid of more delicate apparatus, has shown that, whenever copper and zinc are brought in contact, the copper becomes negative to the zinc. In proof that the chemical action of atmospheric moisture was not the cause of the phenomenon, he showed that, when a drop of water served to connect the copper and the zinc, no charge at all was produced. The fact may therefore be regarded as established, as the result of numerous and varied experiments, that a difference of electrical potential is always developed at the surfaces of contact of heterogeneous media. Not only is this true of solids in contact with solids, but also of solids in contact with liquids, and of liquids in contact with each other. Of course, the production of electricity by contact must result from a loss of energy elsewhere. In the opinion of Cumming, it is the loss of energy which is owing to the unsymmetrical swinging of the molecules on the two sides of the surfaces of contact, which reappears as difference of potential between the solids or as the energy of electrical separation.
But we may carry the sequence yet another step backward. The energy which is thus lost at the surfaces of separation must be heat, and this junction must be cooled thereby. Thus the production of thermo-electricity is seen only to be a special case of a general law, a view to which the well-known Peltier effect gives support. In this phenomenon, when two metals are joined together in the form of a ring and one junction is heated, a current is produced which cools the other junction. From a study of these conditions, Thomson has concluded that the absorption of heat in a thermo-electric circuit varies for different metals with the direction of the current. Thus in iron, the current from hot to cold absorbs heat, while in copper the current which absorbs heat is from cold to hot. In entire accordance with these results are the conclusions recently reached by Hoorweg. Whenever two conductors come into contact, motion of heat results in the development of electricity, the current produced existing at the cost of heat at one part of the point of contact, and evolving heat at the other for a result. Hence all voltaic currents are thermo-currents.
To return to the muscle, it must now be apparent that the electrical charge which appears in its fiber may have its origin in so purely a physical cause as the contact of the heterogeneous substances of which the tissue is built up; the maintenance of this charge being effected by chemical changes going on constantly in the substance of the muscle, by which the carbon dioxide is produced, which is shown to be a measure of the work done.
Conceding, now, that muscular contraction is of the nature of an electric discharge, by what mechanism is the contraction effected? A string of electrified masses, like a muscular fibril, would seem at first to oppose the view now advanced. Such a row of particles would indeed attract each other when electrified and shorten the length of the whole. But the force of contraction would increase as the length diminished; whereas the fact in the case of the muscle is precisely the reverse. Two theories have been advanced to account for the result. The first, proposed by Marey, likens the muscular fiber to a string of india-rubber which, when stretched, contracts upon the application of heat, thus transforming heat directly into work. The other, brought forward and strongly supported by Radcliffe, explains contraction by direct electric charge. Each fiber of the muscle together with its sheath constitutes a veritable condenser, the charge upon the exterior being positive and upon the interior negative. When a charge is communicated to the fiber, lateral compression results from the attraction of the electricities of opposite name, and, since the volume remains constant, elongation is the consequence—precisely as a band of caoutchouc, having strips of tin-foil upon its sides, may be shown to elongate when charged like a condenser. In this view of the matter the normal condition of the muscle is one of charge, of elongation. Contraction results from the simple elasticity of the muscle itself, the function of the nerve being only that of a discharger. Whether this theory represents the actual fact or not, in all its details, it is supported by the existence of rigor mortis, by the continued relaxation of muscle during the flow of the current, by the cessation of contraction on the free access of blood, and by many other phenomena otherwise difficult to explain.
From this brief review, does it not seem probable that the phenomenon of muscular contraction may be satisfactorily accounted for without the assumption of "vital irritability," so long invoked? May it not be conceded that the theory that muscular force has a purely physical origin is at least as probable as the vital theory?
Time would fail me to discuss the many other phenomena of the living body which have been found on investigation to be non-vital. Digestion, which Prout said it was impossible to believe was chemical, is now known to take place as well without the body as within it, and to result from non-vital ferments. Absorption is osmotic, and its selective power resides in the structure of the membrane and the diffusibility of the solution. Respiration is a purely chemical function. Oxyhæmoglobin is formed wherever hæmoglobin and oxygen come in contact, and the carbon dioxide of the serum exchanges with the oxygen of the air according to the law of gaseous diffusion. Circulation is the result of muscular effort both in the heart and the capillaries, and the flow which takes place is a simple hydraulic operation. Even coagulation, so tenaciously regarded as a vital process, has been shown to be purely chemical, whether we adopt the hypothesis of Schmidt that it results from the union of two proteids, fibrinogen and fibrinoplastic substance, or the later theory of Hammarsten, that fibrine is produced from fibrinogen by the action of a special ferment.
One function yet remains which can not be altogether omitted from our consideration. This function is that of the nervous system. In structure, this system is well known to us all. In composition, it is made up essentially of a single substance, discovered by Liebreich and called protagon, the specific characters of which have lately been confirmed by Gamgee. In function, the nerve-cell and the nerve-fiber are occupied solely in the reception and the transmission of energy, which is in all probability electrical. There is evidently a close analogy between the nerve and the muscle, the axis cylinder like the fibrilla being composed of cells, and having a positive electric charge upon the exterior surface, which has a tension of one tenth of a volt. Haughton attributes tinnitus aurium to the discharge of nerve-cells.
The only objection raised to the electrical character of nerve-energy is based upon its slow propagation. Though thirty years ago Johannes Müller predicted that the velocity of nerve transmission never could be measured, yet Helmholtz accomplished the feat very soon afterward. His results, like those of subsequent experimenters, show that the velocity of propagation of the nervous influence along a nerve, like that of electric transmission, is only about twenty-six to twenty-nine metres in a second. But it should be borne in mind, as Lovering has pointed out, that electricity has no velocity, in any proper sense; that, since the appearance of an electrical disturbance at the end of a conductor depends upon the production of a charge, the time of this appearance will be a joint function of the electrostatic capacity of the conductor and of its resistance. Since each of these values is directly proportional to length, it follows that the time of transmission will vary as the square of the length of the conductor. While, therefore, in Wheatstone's experiment, he found that electricity required rather more than one millionth of a second to pass through one quarter of a mile of wire, it does not follow that it would traverse 288,000 miles in one second, as he assumed. Indeed, as Lovering has shown, its actual velocity would be only two hundred and sixty-eight miles in an entire second. Hence the marvelous discrepancies which have been observed in the results of experiments made to determine the velocity of electricity on long wires are explained.
In the nerve itself, therefore, the velocity of transmission may be supposed to be the less as its resistance is greater. Now, Weber has shown that animal tissues in general have a conductivity only one fifty-millionth of that of copper. And Radcliffe found that a single inch of the sciatic nerve of a frog measured 40,000 ohms, a resistance eight times that of the entire Atlantic cable. In experimenting to confirm the above law of velocity, Gaugain measured the time of transmission of the electric current through a cotton thread 1·65 metre long, and found it to be eleven seconds. Two similar threads placed consecutively, thus forming a conductor twice as long, required forty-four seconds for the passage of the current, or four times as long. From these data the velocity in the short thread is at the rate of only 0·15 metre in one second; and in the long one only about half this rate, of course. Hence the fact that the energy of nerve moves at the rate of only twenty-eight metres per second is really no proof that it is not electricity.
The higher functions of the nerve-cell, those connected with mental processes, is a field too vast to be entered at this time. The double telegraph line of nerve, motor and sensor in their effect, but, as Vulpian has proved, precisely alike in function, are the avenues of ingress and egress. Every sensory impression is received by the thalami optici; every motor stimulus is sent out from the corpora striata. In the acts denominated reflex, the action goes from the spinal cord and is automatic and unconscious. Should the impression ascend higher to the sensory ganglia, the action is now conscious, though none the less automatic. Finally, should deliberation be required before acting, the message is sent to the hemispheres by the sensory ganglia, and will operates to produce the act. Based on principles which can be established by investigation, a true psychology is coming into being, developed by Bain, Maudsley, Spencer, and others. A physiological classification of mental operations is being formed which uses the terms of metaphysical psychology, but in a more clearly defined sense. Emotion, in this new science, is the sensibility of the vesicular neurine to ideas—memory, the registration of stimuli by nutrition. Reflection is the reflex action of the cells in their relation to the cerebral ganglia. Attention is the arrest of the transformation of energy for a moment. Ratiocination is the balancing of one energy against another. Will is the reaction of impressions outward. And so on through the list.
Among the physical aspects of the mind-question, the problem of the quantitative changes which take place in the organism is a very curious and interesting one. That the energy of the brain comes from the food will be disputed by no one in these days. Hence, the brain must act like a machine and transform energy. There is, then, a purely physiological representation of mental action, concerned with forces which are known and measurable. The researches of Lombard long ago showed the concomitant heat of mental action. Recent researches are equally interesting, which show that mental operations are not instantaneous, but require a distinct time for their performance. By accurate chronographic measurement, Hirsch has shown that an irritation on the head is answered by a signal with the hand only after one seventh of a second; that a sound on the ear is indicated by the hand in one sixth of a second; and that, when light irritates the eye, one fifth of a second elapses before the hand moves. The mechanism of such a process is the following: Suppose the sound "A" is heard by the ear. After a latent period it is translated to some nerve-cells and hence to the brain. From the brain it goes to other cells, ganglion cells, and to other nerves, and then to the different muscles of the chest and larynx, and then follows the audible response "A." Now, since this whole process requires only one sixth of a second, the question arises, How much of it is psychical? To answer it, the experiment is repeated, but with this difference, that the particular sound to be used is unknown to the experimenter. Before the sound can be repeated by him, therefore, a distinct act of discrimination is required, and the time taken is longer. Calling the time in the first experiment a, and in the second b, the difference b—a is the time required for two distinct actions; one, that of distinguishing the sound, and the other, that of willing the corresponding movement. If, now, it be agreed that only the sound "A" shall be responded to when called, these may be separated, since, no other sound being responded to, the latter action is eliminated. If the time now required be called c, the difference c—a represents the time required for forming a judgment, and c—b the time required for a volition. In making these measurements, Donders used an instrument devised by him, called a noëmotachograph, and also a modification of it, called a noëmotachometer. By these instruments different points of the body can be irritated, different sounds can be produced, and different colors or letters can be shown, all by the electric spark. By subtracting the simple physiological time from the time given in any experiment, the time necessary for recognition may be obtained. By an addition to the apparatus, a second stimulus may be made to follow the first, either on the same or on a different sense, thus enabling the time necessary for a simple thought to be determined. As a result of his experiments, Donders found that the value b—a in the case of a simple dilemma was seventy-five thousandths of a second, this being the time required for recognition and subsequent volition. In the same way c—a has been shown to be forty thousandths of a second, being the time required for simple recognition; there are left thirty-five thousandths of a second as the time required for volition. Moreover, by independent measurement with the noëmotachometer, exactly the same time, one twenty-fifth of a second, is found necessary to enable a judgment to be formed about the priority of two impulses acting on the same sense. If they act on different senses, more time is necessary. So, also, more time is required to recognize a letter by seeing its form than by hearing its sound. A man of middle age, then, thinking not so very quickly, requires one twenty-fifth of a second for a simple thought.
Another important fact concerning nervous action is that its amount may be measured by the quantity of blood consumed in its performance. Dr. Mosso, of Turin, has devised an apparatus called the plethysmograph—drawings of which were exhibited at the London Apparatus Exhibition of 1876—designed for measuring the volume of an organ. The forearm, for example, being the organ to be experimented on, is placed in a cylinder of water and tightly inclosed. A rubber tube connects the interior of the cylinder with the recording apparatus. With the electric circuit, by which the stimulus was applied to produce contraction, were two keys, one of which was a dummy. It was noticed that, after using the active key several times, producing varying current strengths, the curve sank as before on pressing down the inactive key. Since no real effect was produced, the result was caused solely by the imagination, blood passing from the body to the brain in the act. To test further the effect of mental action, Dr. Pagliani, whose arm was in the apparatus, was requested to multiply 267 by 8, mentally, and to make a sign when he had finished. The recorded curve showed very distinctly how much more blood the brain took to perform the operation. Hence the plethysmograph is capable of measuring the relative amount of mental power required by different persons to work out the same mental problem. Indeed, Mr. Gaskell suggests the use of this instrument in the examination-room, to find out, in addition to the amount of knowledge a man possesses, how much effort it causes him to produce any particular result of brainwork. Dr. Mosso relates that, while the apparatus was set up in his room in Turin, a classical man came in to see him. He looked very contemptuously upon it and asked of what use it could be, saying that it couldn't do anybody any good. Dr. Mosso replied, "Well, now, I can tell you by that whether you can read Greek as easily as you can Latin." As the classicist would not believe it, his own arm was put into the apparatus and he was given a Latin book to read. A very slight sinking of the curve was the result. The Latin book was then taken away and a Greek book was given him. This produced, immediately, a much deeper curve. He had asserted before that it was quite as easy for him to read Greek as Latin, and that there was no difficulty in doing either. Dr. Mosso, however, was able to show him that he was laboring under a delusion. Again, this apparatus is so sensitive as to be useful for ascertaining how much a person is dreaming. When Dr. Pagliani went to sleep in the apparatus, the effect upon the resulting curve was very marked indeed. He said afterward that he had been in a sound sleep, and remembered nothing of what passed in the room—that he had been absolutely unconscious; and yet, every little movement in the room, such as the slamming of a door, the barking of a dog, and even the knocking down of a bit of glass, were all marked on the curves. Sometimes he moved his lips and gave other evidences that he was dreaming; they were all recorded on the curve, the amount of blood required for dreaming diminishing that in the extremities. The emotions, too, left a record. When only a student came into the room, little or no effect appeared in the curve; but, when Professor Ludwig himself came in, the arteries in the arm of the person in the apparatus contracted quite as strongly as upon a very decided electrical stimulation.
In an address of the retiring President of this Association, delivered but a few years ago, I find this sentence: "Thought can not be a physical force, because thought admits of no measure." In the light of the rapid advances lately made in investigating mental action, we see that in two directions at least, in its rate of action and of its relative energy, we may already measure thought, as we measure any other form of energy, by the effects it produces.
Passing now to the consideration of the general question of the transformation of energy which is effected by living beings, attention may be called to one or two points in general physics, as bearing upon its solution. The great law of the dissipation of energy, as modified by Thomson from the statement of Clausius, is thus stated: "The entropy of the universe tends to zero." In other words, the energy of the universe available for transmutation is approaching extinction. This conclusion is based upon the fact that while every form of energy can be completely converted into heat, heat can not be completely converted into other forms of energy, nor these into each other. Hence it arises that energy is being gradually dissipated as heat. Moreover, since transformation can only result when heat passes from a higher to a lower temperature, it follows that, when that perfect equilibrium of temperature is reached toward which events are tending, there can be no other energy than heat, and this absolutely inconvertible, irrecoverable. To apply this law to the present case, the muscle, for example, is a machine for transforming the energy of food into work. Since, consequently, this conversion is not complete, it follows that heat must appear as a necessary result of muscular action. The heat of animal life, consequently, is not heat especially provided; it is simply the heat which inevitably results from an incomplete conversion of energy.
Again, the form of chemical action thus far assumed by physiologists to account for the energy of the living animal has been combustion. But the science of thermo-chemistry, as developed in late years by Berthelot and Thomson, has proved that direct union of chemical substances may not only not evolve heat, but may actually absorb it. It appears, too, that thermal changes accompany all forms of chemical change, those of decomposition and exchange as well as those of synthesis. The animal absorbs highly complex substances as food, capable of innumerable stages of retrogressive metamorphosis before elimination. In each of these stages heat is evolved, being the energy successively stored up by the plant when it repeated these stages in the inverse order.
Another point of interest has reference to the modern views of capillarity. In 1838 J. W. Draper showed that capillarity is an electrical phenomenon. Quite recently, Lippmann has developed and extended this view and fully confirmed it. Whenever the free surface of a liquid, curved by capillary action, is electrified it changes its form; and conversely, when such a surface is made by mechanical means to change its form, an electromotive force is developed. Based upon this principle Lippmann constructed a capillary reversible engine and an extremely sensitive capillary electrometer. The former, when a current of electricity was applied to it, developed mechanical work and ran as a motor. When turned by hand, it became an electromotor. In the animal organism there are it is true but a few free surfaces where this action can take place. But Gore has shown that the same phenomenon appears between two liquids in contact, their boundary being altered in character by electrification. Indeed, when we consider the production of electricity by osmose, and of heat and electricity both by inhibition, both capillary phenomena, the wonder is not that so much energy is evolved by the organism, but that it is so little. If the physical and chemical changes which take place within the body took place without it, there would be an abundant evolution of energy. Can we doubt that these changes are the cause of the energy exhibited by the organism?
Thus far, when we have spoken of a living being, we have had reference to the organism as a whole, and this of a rather complex kind. In this view of the case, however, we find that biological microscopists do not agree with us. "The cell alone," says Küss, "is the essentially vital element." Says Beale: "There is in living matter nothing which can be called a mechanism, nothing in which structure can be discerned. A little transparent, colorless material is the seat of these marvelous powers or-properties by which the form, structure, and function of the tissues and organs of all living things are determined." And again, "However much organisms and their tissues in their fully formed state may vary as regards the character, properties, and composition of the formed material, all were first in the condition of clear, transparent, structureless, formless living matter." So Ranvier: "Cellular elements possess all the essential vital properties of the complete organism." And Allman, in his address as President of the British Association last year, is still more explicit. "Every living being," he says, "has protoplasm as the essential matter of every living element of its structure. . . . No one who contemplates this spontaneously moving matter can deny that it is alive. Liquid as it is, it is a living liquid; organless and structureless as it is, it manifests the essential phenomena of life. . . . Coextensive with the whole of organic nature—every vital act being referable to some mode or property of protoplasm it becomes to the biologist what the ether is to the physicist." From these quotations it would seem that even in the highest animal there is nothing living but protoplasm or germinal matter, "transparent, colorless, and, as far as can be ascertained by examination with the highest powers of the microscope, perfectly structureless. It exhibits these same characters at every period of its existence." Neither the contractile tissue of the muscle, the axis-cylinder of the nerve, nor the secreting cell of the gland, is living, according to Beale. Hence it would be fair to draw the inference that no vital force should be required to explain the phenomena of the non-living matter of the body, such as the contraction of the muscle or the function of the nerve. If this be conceded, it is a great point gained; since the phenomenon of life becomes vastly simplified when we have to account for it only as exhibited in this one single form of living matter, protoplasm. In describing its properties, Allman includes this remarkable mobility, these spontaneous movements, and says: "They result from its proper irritability, its essential constitution as living matter. From the facts there is but one legitimate conclusion, that life is a property of protoplasm." Beale, however, will not allow that life is "a property" of protoplasm. "It can not be a property of matter," he says, "because it is in all respects essentially different in its actions from all acknowledged properties of matter." But the properties of bodies are only the characters by which we differentiate them. Two bodies having the same properties would only be two portions of the same substance. Because life, therefore, is unlike other properties of matter, it by no means follows that it is not a property of matter. No dictum is more absolute in science than the one which predicates properties upon constitution. To say that this property exhibited by protoplasm, marvelous and even unique though it be, is not a natural result of the constitution of the matter itself, but is due to an unknown entity, a tertium quid, which inhabits and controls it, is opposed to all scientific analogy and experience. To the statement of the vitalist that there is no evidence that life is a property of matter, we may reply with emphasis that there is not the slightest proof that it is not.
Chemistry tells us that complexity of composition involves complexity of properties. The grand progress which organic chemistry has made in recent times has been owing to the distinct recognition of the influence of structure upon properties. Isomerism is one of its most significant developments. The number of possible isomers increases enormously with the complexity of the molecule. Granted that we now know several of the proteid group of substances: how many thousands may there be yet to know? Bodies of such extreme complexity of constitution may well have an indefinite number of isomers. Not only does Chemistry not say that there can not be such a thing, but she encourages the expectation that there will yet be found the precise proteid of which the changes of protoplasm are properties. The rapid march of recent organic synthesis makes it quite certain that every distinct chemical substance of the living body will ultimately be produced in the laboratory; and this from inorganic materials. Given only the exact constitution of a compound, and its synthesis follows. When, therefore, the chemist shall succeed in producing a mass constitutionally identical with protoplasmic albumen, there is every reason to expect that it will exhibit all the phenomena which characterize its life; and this equally whether protoplasm be a single substance or a mixture of several closely allied substances.
But here a word should be said concerning a remarkable physical condition assumed by matter in organized beings. Graham, in 1862, drew the sharp line which separates colloid from crystalloid matter. "His researches have required," says Maudsley, "a change in our conception of solid matter. Instead of the notion of inert, impenetrable matter, we must substitute the idea of matter which in its colloid state is penetrable, exhibits energy, and is widely susceptible to external agents. This sort of energy is not a result of chemical action, for colloids are singularly inert in all ordinary chemical relations, but is a result of its unknown molecular constitution; and the undoubted existence of colloidal energy in organic substances, which are usually considered inert and called dead, may well warrant the belief of its larger and more essential operation in organic matter in the state of instability of composition in which it is when under the condition of life. Such energy would then suffice to account for the simple uniform movements of the homogeneous substance of which the lowest animal consists, and the absence of any differentiation of structure is a sufficient reason for the absence of any localization of function and of the general uniform reaction to local impressions." Graham himself says: "The colloidal state may be looked upon as the probable primary source of the force appearing in the phenomena of vitality." The colloidal condition is the dynamical state of matter; the crystalloidal the static. The former, which is the rule in the organic kingdom of nature, is the exception in the inorganic. Aluminum and ferric hydrates, silicic acid, and a few other inorganic substances, exist in the colloid condition. From analogy there would seem to be but little doubt that the colloid state of these bodies differs from their crystalloid state merely in the size of the molecule. In other words, opal, which is colloid silica, is a polymer of quartz. If this theory be true, there can be no doubt of the vastly greater complexity of a colloidal proteid molecule than of a crystalloid one. Now, it is a very significant fact, in this connection, that not a single organic colloid has ever been synthesized. Gelatine, which is one of the best examples of a colloid, has a comparatively simple structure. And, although Gibbs showed, many years ago, that gelatine was probably an amido-derivative of the sugar group, yet no inverse process has yet given us this substance. That matter in the crystalloid and the colloid forms may be chemically identical, differing only in the size of its molecule, may be quite possible. But it is also possible that the difference may be a physical one. To produce the colloid state from the crystalloid is by no means beyond the power of science. We qualify our previous statement, then, only so far as to say that when the chemist produces a body in the colloidal form, having the identical constitution of protoplasm, there is every reason to believe that it will have the properties of protoplasm.
The important question now arises whether, since the protoplasm of animals is identical with that of vegetables, and the latter is the food of the former, any protoplasm whatever is vitalized by the animal as such. That this identity exists would seem satisfactorily established. Though the protoplasm of vegetables is inclosed within a cellulose bag, it is only a closely imprisoned rhizopod. In the Nitella, it shows all its characteristic irritability, and from Vaucheria it escapes to exhibit all its amoeboid movements. Spores swim about by cilia or flagella, and the cell-division of the one kingdom is the same as that of the other. In plants, however, protoplasm seems to be associated with chlorophyl, whose function was for a long time supposed to be to decompose carbon dioxide under the influence of sunlight. But Draper in 1843 showed that this decomposition took place before the chlorophyl was formed. Recent researches have shown that the function of chlorophyl is wholly protective. The assimilative power of the protoplasm reaches its maximum in the orange and yellow rays. Now, Bert has shown that the absorption band in the chlorophyl spectrum is in the exact position of this maximum. Hence, Gautier believes that this substance acts as a regulator of plant respiration, the greater or less amount of luminous energy thus absorbed and transformed being utilized by the protoplasm and stored up. Growth and cell-division, however, are independent of orange light and hence of chlorophyl. In the higher plants these functions are performed by a separate and deep-lying set of cells. But, in the lower, the same cell discharges both functions, assimilation going on in it during the day, and growth chiefly at night. Sachs had already proved that the maximum growth of plants takes place just before daylight, and the minimum in the afternoon. This retarding action of sunlight upon growth is as curious as it is unexpected. It now appears that in orange light plants assimilate—absorb carbon dioxide and evolve oxygen—but do not grow—are not heliotropic; while in blue light they are strongly heliotropic, but do not give off oxygen. Chlorophyl, however, is not confined to vegetables; infusoria, hydras, and certain planarian worms are green from the presence of this substance, and Geddes has shown that such animals placed in the sunlight give off a gas which is more than half oxygen. These cells, moreover, contain starch-granules.
A still more striking evidence of this intimate relationship has been developed by Darwin, in his researches upon insectivorous plants. Not only do these plants possess a mechanism for capturing insects, but they secrete a gastric juice which digests them. Nägeli has shown the presence of pepsin in yeast-cells, and attention has lately been called by Wurtz and others to the juice of the Carica papaya, which contains a pepsin-like substance capable of peptonizing fibrine completely. Moreover, there is the closest similarity between diastase and ptyaline; and the milk of the cow-tree, recently examined by Boussingault and found to resemble cream closely in composition, shows the presence of an emulsifying agent in the vegetable kingdom analogous to pancreatine in the animal.
Another most curious proof of the identity of animal and vegetable protoplasm has been given by Claude Bernard, who has shown that both are alike sensitive to the influence of anæsthetics. A sensitive plant exposed to ether no longer closed its leaflets when touched. Assimilation and growth, as well as germination, are arrested by chloroform. The yeast-plant when etherized no longer decomposes sugar to produce alcohol and carbon dioxide; while the inversive and non-vital ferment still acts to convert the cane-sugar into glucose; precisely as under these circumstances the diastasic ferment converts the starch of the seed into sugar. By arresting anæsthetically the process by which carbon dioxide is absorbed and oxygen evolved, the true respiratory process, being less affected, now appears; and Schützenberger has proved that the fresh cells of the yeast-plant breathe like an aquatic animal.
It would seem, then, that the protoplasmic life of animals is identical with that of plants; a certain measure of destructive metamorphosis taking place in each, evolving energy and producing carbon dioxide and water. When, however, this function is examined quantitatively, its maximum is seen to be reached in the animal. While the assimilative function characterizes the plant, the destructive function distinguishes the animal. Hence it is the function of the plant to store up energy to produce the highly complex protoplasm. This, consumed by the animal as his food, continues his existence as a living being, the energy gradually set free by its successive steps of retrogressive metamorphosis appearing as the work which he performs. If this view be correct, it would follow that every individual substance found in the animal—save only those which result from degradation—must be found in the plant upon which it feeds, and this is the fact. The myosine which Kühne has shown to be the distinctive proteid of muscle, Vines has found in the aleuron-grains of the lupine and the castor-oil plant, along with vitelline, the special proteid of the vitellus. The researches of Weyl and Bischoff have proved that gluten is formed in the dough of wheat-flour by the action of a ferment upon the globuline-substance or plant-myosine which it contains, precisely as Hammarsten has shown fibrine is produced in the action of a similar ferment upon fibrinogen. Not only this; Hoppe-Seyler has extracted from maize the identical substance which has been shown by Liebreich to be the essential chemical constituent of nerve-tissue, protagon.
The evidence, then, would seem conclusive that, since the protoplasm of the animal and the vegetable kingdoms is identical, the former in all cases being derived from the latter, the animal as such neither produces nor vitalizes any protoplasm. Two inferences seem naturally to follow from this conclusion: 1. That all the properties of animal protoplasm, and of the animal organism of which it constitutes the essential part, must have a previous existence in the plant; 2. That hence the solution of the life-question in the Myxomycetes will solve the life-problem for the highest vertebrate.
Another consideration which must not be left out of the account in any discussion of the life-question is the potent influence of environment. Ordinary examples of this influence pass before our eyes every day. Heat necessitates the germination of the seed, and light causes the plant to grow. Gravity obliges its root to grow downward and its stem to ascend. Certain sensations from without excite inevitably muscular contraction; and a ludicrous idea may provoke laughter in defiance of the will. Epidemic and epizoötic diseases show the dependence of function upon external conditions, and the germ theory demonstrates the utter disproportionality of the cause to the effect. The remarkable similarity in the periodicity observed between sunspots and the weather has been extended to include the appearance of locusts and the advent of the plague. Even the body politic feels its influence, Jevons having established a coincident periodicity for commercial crises.
The modern theory of energy, however, puts this influence in a still stronger light. As defined hitherto, energy is either motion or position; is kinetic or potential. Energy of position derives its value obviously from the fact that in virtue of attraction it may become energy of motion. But attraction implies action at a distance; and action at a distance implies that matter may act where it is not. This of course is impossible; and hence action at a distance, and with it attraction and potential energy, are disappearing from the language of science. But what conception is it which is taking its place? By what action does the sun hold our earth in its orbit? The answer is to be found in the properties of the ether which fills all space. The existence of this ether, the phenomena of light and electricity abundantly prove. While so tenuous that astronomy has been taxed to prove that it exerts an appreciable resistance upon the least of the celestial bodies, its elasticity is such that it transmits a compression with a wellnigh infinite velocity. On the one hand, Thomson has determined its inferior limit, and finds that a cubic mile of it would weigh only one thousand millionth of a pound; on the other, Herschel has calculated that, if an amount of it equal in weight to a cubic inch of air be inclosed in a cubic inch of space, its reaction outward would be upward of seventeen billions of pounds. Instead of being represented, as is our air, by the pressure of an homogeneous atmosphere five miles in height, such a pressure would represent just such an homogeneous atmosphere five and a half billions of miles high, or about one third the distance to the nearest fixed star! In Herschel's own words, "Do what we will, adopt what hypothesis we please, there is no escape, in dealing with the phenomena of light, from these gigantic numbers, or from the conception of enormous physical force in perpetual exertion at every point throughout all the immensity of space."
Now, as Preston has suggested, if we regard this ether as a gas, defined by the kinetic theory that its molecules move in straight lines, but with an enormous length of free path, it is obvious that this ether may be clearly conceived of as the source of all the motions of ordinary matter. It is an enormous storehouse of energy, which is continually passing to and from ordinary matter, precisely as we know it to do in the case of radiant transmission. Before so simple a conception as this, both potential energy and action at a distance are easily given up. All energy is kinetic energy, the energy of motion. In a narrower sense, the energy of matter-motion is ordinary kinetic energy; the energy of ether-motion, which may become matter-motion, fills the conception of the older potential energy. Giving now to the ether its storehouse of tremendous power, and giving to it the ability to transfer this power to ordinary matter upon opportunity, and we have an environment compared with which the strongest steel is but the breath of the summer air. In presence of such an energy it is that we live and move; in the midst of such tremendous power do we act. Is it a wonder that out of such a reservoir the power by which we live should irresistibly rush into the organism and appear as the transmuted energy which we recognize in the phenomena of life? Truly, as Spinoza has put it, "Man thinks himself most free when he is most a slave."
Such, now, are some of the facts and fancies to be found in the science of to-day concerning the phenomena of life. Physiologically considered, life has no mysterious passages, no sacred precincts into which the unhallowed foot of Science may not enter. Research has steadily diminished day by day the phenomena supposed vital. Physiology is daily assuming more and more the character of an applied science. Every action performed by the living body is sooner or later to be pronounced chemical or physical. And when the last vestige of the vital principle shall disappear, the word "Life," if it remain at all, will remain to us only to signify, as a collective term, the sum of the phenomena exhibited by an active organized or organic being.
I can not close without speaking a single word in favor of a vigorous development in this country of physiological research. What has already been done among us has been well done. I have said with diffidence what I have said in this address, because I see around me those who have made these subjects the study of their lives, and who are far more competent to discuss them than I am. But the laborers in the field are all too few, and the reasons therefor are not far to seek. One of these undoubtedly is the high scientific attainment necessary to a successful prosecution of this kind of investigation. The physiological student must be a physicist, a chemist, an anatomist, and a physiologist, all at once. Again, the course of instruction of those who might fairly be expected to enter upon this work, the medical students of the country, is directed toward making them practitioners rather than investigators. In the third place, the importance of physiological studies in connection with zoölogical research is only beginning in this country to receive the share of attention it deserves. I well remember the gratification I experienced in 1873 upon receiving a letter from Professor Louis Agassiz, asking me to give some lectures at Penikese upon physiological chemistry—a new departure for those times. In this view of the case it seems very appropriate that a new subsection of this Association should be just now in process of formation. We welcome warmly the body of men who form it, and we predict that from the new subsection of Anatomy and Physiology most valuable contributions will be received for our proceedings.
It is a beautiful conception of science which regards the energy which is manifested on the earth as having its origin in the sun. Pulsating awhile in the ether-molecules which fill the intervening space, this motion reaches our earth and communicates its tremor to the molecules of its matter. Instantly all starts into life. The winds move, the waters rise and fall, the lightnings flash, and the thunders roll, all as subdivisions of this received power. The muscle of the fleeing animal transforms it in escaping from the hunter who seeks to use it for the purpose of his destruction. The wave that runs along that tiny nerve-thread to apprise us of danger transmutes it, and the return pulse that removes us from its presence is a portion of it. The groan of the weary, the shriek of the tortured, the voiced agony of the babeless mother, all borrow their significance from the same source. The magnificence of the work of a Leonardo da Vinci or a Michael Angelo; the divine creations of a Beethoven or of a Mozart; the immortal "Principia" of a Newton, and the "Mécanique Céleste" of a Laplace—all had their existence at some point of time in oscillations of ether in the intersolar space. But all this energy is only a transitory possession. As the sunlight gilds the mountain-top and then glances off again into space, so this energy touches upon and beautifies our earth and then speeds on its way. What other worlds it reaches and vivifies we may never know. Beyond the veil of the seen, Science may not penetrate. But Religion, more hopeful, seeks there for the new heavens and the new earth, wherein shall be solved the problems of a higher life.