Popular Science Monthly/Volume 24/April 1884/Physiological Significance of Vital Force
|PHYSIOLOGICAL SIGNIFICANCE OF VITAL FORCE.|
MODERN science has so extended the horizon of our mental perspective, has achieved such brilliant triumphs in so many departments of thought, and, on the basis of verified fact, has erected such an imposing superstructure of useful knowledge in the domain of inorganic nature, that some, rejecting the vitalistic theories of the past, have accepted the belief that the deeper mysteries of vital phenomena will, in a final analysis, be demonstrated to be but resultants of physical forces acting under the complex conditions of organization.
To investigate and interpret the varied phenomena of nature is the unquestioned prerogative of the human intellect; but science, having to do only with "particular orders of phenomena which exist in relation to the percipient mind" and are susceptible of verification, does not hope to solve the profound mysteries involved in the ultimate realities of either matter, energy, or life. With restless energy the human mind presses on in its search for truth, and brings from varied sources new facts to add to the sum of knowledge, until the conclusion is reached that matter is indestructible and energy persistent, and in the formulated laws of the "correlation and conservation of energy" the widest generalizations are made. In thus classifying and uniting the manifestations of matter and of life, whether morphological or physiological, under one general cosmic law, their explanation is made complete within the limits of the known.
Phenomena are explained, but the absolute remains unrevealed. The questions still are asked: What is gravity? What are chemical, electrical, and vital forces? What is the essential nature of matter, energy, and life? There is no oracle to answer.
The study of vital phenomena is difficult because of their complex character, and, in the absence of exact analysis, speculative philosophy has for many ages ventured different theories in explanation of their nature. In seeking to give the present status of physiological science on this important question, it is of interest to take a general historical retrospect, in order that the steps of progress may be observed.
The atomic philosophy, as taught by Democritus and Epicurus, recognized but one kind of matter, whose elements, by virtue of their various forms, had the property of diversified and endless combinations. This play of atoms, independent of an overruling intelligence, produced the worlds of inorganic and of organized matter, which move on in endless cycles and are obedient only to physical forces.
Plato regarded the intelligent soul as of dual character: one part, located in the body, being mortal and presiding over the appetites and passions; the other part, located in the head, being immortal and the source of reason.
The nature of the function of the brain and of the nervous system was unknown to Aristotle, who thought the soul contained the body having its mortal part located in the heart. He, as well as Plato, thought the "pneuma," or breath, was to cool the blood, and in some way act as an instrument of mind over bodily actions. The vital principle of all life-forms resides in a germ; "this principle, while it resembles heat, is not fire, but a spirit similar in nature to the sun and stars."
Hippocrates accepted the Pythagorean doctrine of the four elements, and from it developed his theory of four principal "humors" of the body. He taught the existence of an "intermediate nature," which, though distinct from the mortal soul or pneuma, was the source of vital activity.
The pneuma was deemed such an important factor in the explanation of vital phenomena, that a school called "Pneumatists" was founded in the first century of our era. It was not then known that the arteries contained blood, but they were regarded as the channels through which the pneuma passed throughout the body; and this pneuma was to Galen, A.D. 130, identical with the soul. For fourteen hundred years "pneumatism," under varied forms, was the accepted philosophic belief of the civilized world, and only in the latter part of the sixteenth century did anatomical study enable Sylvius, Fallopius, Fabricius, and Harvey, to modify the prevailing belief of bodily functions. Then it was that Paracelsus sought to explain vital phenomena through the agency of an "archæus" or demon, which, he affirmed, was located in the stomach, and presided over the processes of nutrition, separating the useful from the poisonous part of the food.
Van Helmont adopted the idea of an archæus, but thought it an immaterial though personal force or entity, which "presided over all bodily functions" and gave to each member of the body its own special "vital spirit." The consensus of all these vital spirits produced health, and their disagreement disease.
Van Helmont "discovered gaseous substances and identified the archæus itself with gas." He proclaimed the existence of a general bond of sympathy throughout the universe, because of the "vital spirits" which resided in all forms of matter.
Descartes regarded the body simply as a complex machine, acting under conditions of physical forces, and all the phenomena of life were but the products of their working. The soul, however, was aand independent principle which, located in the pineal gland, made itself known by thought, and took its temporary abode in the body, simply as a spectator of vital functions.
Leibnitz, while admitting a harmony established by Divine power, denied to soul and body any reciprocal influence, saying: "The body goes on in its development mechanically, and the laws of mechanics are never transgressed in its natural motions. Everything takes place in souls as though there were no body, and in the body everything takes place as though there were no soul."
Lord Bacon accepted the doctrine of "vital spirits" as applied to both animate and inanimate bodies.
Glisson believed in "vital spirits intermediate between the soul and organs," and regarded "irritability as a force of which perception and appetite are factors."
Stahl, in the eighteenth century, enunciated the doctrine that chemical forces and vital force not only differ from each other, but are antagonistic. Chemical forces are destructive of the living body, and are held in abeyance, and their disintegrating power is neutralized by a vital force which resides in the body and ministers to its functions. "This vital force, struggling against physical force, acts intelligently, upon a definite plan, for the preservation of the organism"; its triumph secures life, while the rule of the physical forces alone brings death. The theories of "vitalism" and "animism" thus took their places among the philosophic ventures of the age.
Borden, Barthez, and Grimaud, "representing the school of Montpellier," accepted "vitalism" but rejected "animism." The principle of life was believed to be distinct from the soul, though it was thought to operate independently of mechanical or chemical laws.
Haller inaugurated the inductive method in physiological science, and, by experiments, located irritability in the muscular tissue and sensibility in the nervous tissue.
Buffon explained vital phenomena through the instrumentality of "organic molecules" which, differing in form and nature, were indestructible and endowed with the "properties of vitality." These molecules, when associated, not only gave specific character to each part of the organism, and provided for its physiological activity, but became the perennial source of life.
In order to explain how the organic molecules became arranged into the specific forms of life, and preserved individual and type identity in nutrition and reproduction, Buffon projected his theory of "interior molds," by which, in connection with the "organic molecules," he sought to account for all the phenomena of the organic world. It was not until 1827, when the ovule in the ovarian follicle of mammalians was discovered by De Baer, that the theory of "organic molecules" and "interior molds" was overthrown. A single demonstrated fact destroyed the speculations of an age.
Bonnet's theory of "included germs" was another example of reasoning from premises that had not been verified, and the result was disastrous to the subjective method. He taught that the germs of all life-forms not only pre-existed in their first-created representative, but actually contained within themselves, already formed, all the parts of the future organism.
Logical deduction and scientific research, according to the beliefs and methods of the age, permitted such doctrines to receive for a time the approval of popular assent. But the spirit of inquiry was abroad in the world, and the advance of embryological science soon gave the demonstration that the doctrine of "included germs" had no foundation in fact, and so it was numbered with the errors of the past.
Cuvier, who had with such ability compared the structure of animal organs, and classified the facts of animal life in their statical or anatomical relationship, was a "vitalist," and thought the vital properties of the body a kind of entity—independent of physical or chemical forces.
Bichat sought, by a study of the tissues which composed the organs, to learn the nature of their functions, or the dynamics of the living body. He found that all the various kinds of tissue of the body, though differing in function, were endowed with two common properties—extensibility and contractility.
While he made phenomena depend on the properties of matter, he nevertheless followed Stahl as a "vitalist," and claimed that vital and physical properties are not only distinct from but antagonistic to each other: "The vital properties preserve the living body by counteracting the physical properties that tend to destroy it." Each class of phenomena is under distinct laws, and the conflict between them is active and constant. As one or the other triumphs, life or death results, and "health and disease are but the vicissitudes of the strife."
Life is, by Bichat, defined as "the group of functions that resist death," and is under the direct supervision of a special principle called at different times "soul," "archæon," "psyche," or "vital force." The philosophic theory which postulated this undetermined factor was known by the generic term of "vitalism," which, under Stahl and Bichat, took accurate definition, and deeply impressed its tenets upon the physical, chemical, and physiological sciences of the age.
Entities of some kind presided over the functions of life and the manifestations of matter. A "vital principle" ruled the organic world, and the phenomena of inorganic nature depended upon the presence of some "principle" which existed independent of the matter through which it displayed itself. Material particles, darting from luminous bodies into the eye, produced the sensation of light. Heat and cold depended upon the presence or absence of a material substance called "caloric." Electricity was a subtile, material agent, existing in a "latent" state in all substances, and manifesting great power when liberated from its repose. And so throughout the domain of chemical, physical, and biological phenomena, material entities existed and were manifested in all forms of inorganic and organic bodies, and yet were independent of them.
This was not an age for synthetic work; indeed, not even accurate analytic work, except in simple things, could be performed. These are possible only when facts have been observed, and definite knowledge has been acquired in special directions. In the sixteenth century, alchemy, having failed to discover the philosopher's stone, sought to find chemical remedies for diseases. Crude theories were supported by a few facts wrongly interpreted.
Early in the seventeenth century Glauber states that salt is the origin of all things. Boyle argues against the theory that "salt, sulphur, and mercury are the principles of things," and makes heat a powerful factor in originating new bodies. Becher thought that metals consisted of earth, of which there were three kinds—fusible or stony, fatty or fluid, and a "something of which they became deprived on ignition." This "something" Stahl named "phlogiston," which is akin to "spirits" and "souls" of the alchemists.
The phlogistic theory of Stahl was without foundation in fact, and yet, based upon experimental data, it was a step upward in chemical research, and held the minds of all for over one hundred and fifty years, including such great names in the eighteenth century as Hales, Black, Scheele, Priestley, Cavendish, and Lavoisier. Then it was that the analytic method became more accurate. Black, with the balance, demonstrated that the ignition of the metals magnesium and calcium gave no evidence that a ponderable "caloric" entered into them, but, to the contrary, a peculiar "fixed air" was expelled from them, which rendered them lighter than before they were burned.
The foundation of quantitative chemistry was thus laid, and the existence of "imponderable" agents in nature questioned. The discovery of "dephlogisticated air" by Priestley, the investigation of gases by Cavendish, of heat and fire by Scheele, and of insoluble minerals by Bergman—by means of the blow-pipe—were important additions to chemical knowledge, and enabled Lavoisier to generalize the facts already discovered. He announced a new theory of combustion, and, by questioning the existence of phlogiston, and showing that "principles should not be assumed where they could not be detected," revolutionized chemistry and gave it a new impulse, which has been quickened by every discovery since made.
Analysis of inorganic bodies increased, new facts accumulated, and new interpretations of phenomena were given, until the atomic theory, first suggested by Dalton in 1804, was promulgated under the great generalization known as the law of Avogadro or Ampère, which makes "equal volumes of all substances, when in a state of gas, and under like conditions, contain the same number of molecules."
This was the birth of modern chemistry, and, though it received attention when first enunciated in 1811, its far-reaching principles of truth were neither fully understood nor accepted for half a century afterward.
Chemistry, free from the errors of the past, now seeks to discover in the organic world the relations of different substances, as it has sought to know their relations in inorganic nature, and already the evidence is prophetic of wonderful results.
In physical philosophy, "Stahlism" received its mortal wound at the close of the last century by the experiments of Rumford and Davy, which negated the theory of "caloric" and demonstrated heat to be a "mode of motion."
This new doctrine, though founded on a demonstrated fact, was not complete until 1850, when Joule, having determined the mechanical equivalent of heat and established the law of thermo-dynamics, made possible the classification of facts determined by Young, Melloni, Faraday, Liebig, Mayer, Grove, Helmholtz, Carpenter, Tyndall, Henry, and others, which enabled the deduction to be made of the universal laws of the "correlation and conservation of energy."
In inorganic nature, unity, under law, is an accepted fact, and analysis and synthesis harmonize as to causes and effects; but in the organic world there are yet many unknown quantities, and the progress in solving the mysteries of life-action is necessarily slow, because of their complex character.
To some, "vitalism" yet maintains its position in the philosophic realm of organization, and a "vital force," independent of and antagonistic to physical force, yet presides over the manifestations of organic bodies. This, if true, necessitates "two distinct sciences and two disinct orders in nature," which, though related, are not reciprocal. This view is not in harmony with either chemical, physical, or biological science of the present day, and stands in direct contradiction to the accepted doctrine of the correlation and conservation of energy.
Whatever may be the essential nature of the ultimate life-principle—with which science has nothing to do it can not be denied that life-phenomena are presented to us only through forms of matter. Matter, or material organization, is, therefore, so far as human knowledge goes, an absolute condition upon which all life-manifestations depend, and to assert, as do the "vitalists," that this vital energy an agency which can not be verified, though dependent upon a material condition for a display of its action is not related to it, but is independent of it and under distinct and antagonistic laws, is an assumption at variance with scientific truth and reason.
Doubtless one common source of error in the minds of the disciples of "vitalism" is inaccurate definition, confounding, as they do, the scientific meaning of a term with its philosophical or metaphysical significance. Thus, the term "life," when applied to the higher animals, is, to the metaphysical philosopher, often related to, or made synonymous with, the "soul"; while to the physiologist it refers only to the sum of phenomena arising in organized bodies. If what "can not be explained by chemistry or physics" constitutes the vital functions, then, by simply eliminating the known or non-vital factors, we may easily learn the exact amount of the vital element.
Science has already "banished the vital force from the entire province of organic chemical compounds, proving them to be subject to the same physical and chemical forces which determine the composition of mineral matter," and it now remains to test by analysis and synthesis the problem of organization itself.
It may very properly be asked, If the vital force has been banished from the entire province of organic chemical compounds, as asserted and demonstrated, in what it now resides, where is it located and what are its functions?
Chemical science has already demonstrated that all "proximate principles" and tissues of an organized body are, in an ultimate analysis, reducible to some of the elementary substances; and as, in inorganic bodies, morphological differences result from the various combinations of the ultimate elements, so, too, is it with organized bodies. So far as form alone is concerned, it is no more difficult to understand why organic compounds, under conditions of vital relations, take on the special form of a single speck of bioplasm in one case, of a vegetable in another, or of an animal form in another case, than it is to understand why the same elements will produce substances either allotropic or isomeric.
The phenomena are classified and thus explained, but in neither example is the ultimate nature or condition which causes the morphological difference known. There is no known force in nature capable of lifting the elements to the plane of animal organisms, except through the intermediate planes of the mineral and the vegetable kingdoms. Chemism is sufficient to form the mineral kingdom from the simple elements, which are under physical force alone. As the elementary combinations necessary to form a mineral involve an expenditure of force, which is transformed from a lower to a higher expression, so, in resolving the mineral back again to its elementary state, the force conserved in a higher state represents the original larger but weaker force of lower grade. The same is true when chemical compounds, as represented in the mineral kingdom, are lifted to the plane of the vegetable kingdom, or when the members of this class are raised to the highest class of the animal kingdom. In all cases the higher conditions depend upon the conditions of the next lower plane; and the conserved forces of the higher plane, when liberated by decomposition, represent the special functions of the organization.
There is not a phenomenon in animal life, from the earliest stage of germ-growth to the final stage of human development, but is susceptible of classification. The monera—mere specks of bioplasm—organisms without organs, so far as can be determined in their power to move, to receive nourishment, to react on external impressions and to reproduce their kind—not only manifest the fundamental properties of life, but display them under conditions so simple, so free from all morphological complications, that the way seems prepared by nature herself for the inquirer to enter the portals which open into the mysteries of life. They are on the border-land of the living and the not-living, blending on the one side with colloidal matter and on the other with vegetable forms, all so intimately related with simple "matter" as to justify if not necessitate the conclusion of genetic correlation.
We see this simple hyaline particle of bioplasm expand and contract, accompanied with chemical composition and decomposition, and the conclusion is irresistible that these simplest forms of motion, expansion and contraction, follow in orderly sequence of cause and effect.
Motility, arising from chemical disintegration and reintegration, represents, therefore, a fundamental expression of living organized matter, and impresses us with the idea of energy transformed. Indeed, all the functions of the higher organisms testify to the truth of the proposition that every manifestation of energy of organized bodies has its mechanical equivalent, and follows an orderly sequence of events.
The nutrition of the body, through all the intricate processes of external and internal digestion under the action of the digestive ferments, involves only physical and chemical forces in the transformation of the various foods received. The entire animal body is composed of modified protoplasm, as represented in the three classes known as proteids, carbohydrates, and fats, with their respective derivatives.
The proteids are exceedingly complex in character, and are not as yet definitely classified among organic compounds. They unite with acids and alkalies, and yet "do not play the part of an acid toward the base," or conversely. They are not crystallizable, and, having no combining equivalent, do not possess an absolute ultimate constitution, and therefore their molecular reactions and changes in the body can not be expressed by exact chemical symbols.
Here, then, we see the formidable list of "proximate principles" that are known to belong to the animal body as nutrient elements, and which are necessary for tissue development. They are all organic compounds, from which science has "banished the vital force" by "proving them to be subject to the same physical and chemical forces which determine the composition of universal matter." "Where, then, shall we seek this "indefinable something" which exists and acts in the organism independent of and antagonistic to the physical and chemical forces of nature, as affirmed by the doctrines of "vitalism" taught by Stahl and Bichat?
The position held by these distinguished men and their followers has been demonstrated to be untrue, because, whatever may be the essential nature of this vital force, certain it is that it is known only by and through its manifestations. These present themselves to the mind only through organizations which immediately depend on chemical and physical forces for those proximate constituents which go to nourish and build up the tissues and enable the organs of the body to perform their respective functions.
In nutrient action, by which lifeless material or pabulum is transformed into living tissues, evidence of this vital entity should be discovered, if anywhere, for here we have the primal seat of life, the very fountain of genetic power.
Analysis, however, finds room for it in nutrient action no more than in the mysteries which lie concealed in every expression of energy throughout nature's domain. Why will friction of glass produce a condition or property which will repel pith-balls, while friction of sealing-wax produces a condition which will attract them? Are these movements caused by some kind of life-principle developed in so simple a way? No; they come from positive and negative electricity evolved by friction, and, with this answer, science asserts that the explanation is complete. When asked, What is electricity, beyond a special display of energy? there is no answer.
If we question the various organic functions of the body, physical and chemical forces alone confront us. A muscle contracts according to mechanical laws, and its work is expressed in mechanical equivalents. Electric tension is lost, heat is evolved, carbon dioxide appears, and the muscular tissue, before neutral in reaction, is now acid. Whatever may be the nature of the vital force, if such there be, operating in muscular contraction, it at least is not independent of physical and chemical forces, and the evidence is cumulative that these will alone explain the phenomenon. Respiration is purely a chemical process, in harmony with the laws of gaseous diffusion. Circulation, with its pumps, pipes, and valves, is an hydraulic operation. Absorption is osmotic, and a similar selective affinity for special things is exhibited in inorganic material as well as in animal membranes.
There seems no good reason why we should hesitate to regard the vital force as correlated with the physical forces known to us as heat, light, electricity, and actinism. That some relation exists there can be no doubt, for the effect of physical forces upon organic life is marked, and their energy is made potential in the tissues of both vegetables and animals. This potential energy is, after a time, transformed into active energy, and new phenomena result.
Organic forms do not generate energy, they simply transform or evolve it from that which has been supplied from the outer world. Heat in the body results from combustion the same as in a furnace.
Contractility is a special function of muscular tissue, and is independent of nerve-force. This attribute exists in the tissue for a time after death, lasting longer in cold-blooded than in warm-blooded animals, because of the slowness of the process of the destructive assimilation of the tissues. Longet demonstrated that contractility is closely related to the supply of arterial blood in the capillary vessels, for, on diminishing the supply, contractility was lessened, and the temperature of the muscles reduced; while Matteucci proved that increased heat accompanies muscular contraction. The heat produced by muscular contraction is divided into two complementary portions, one part appearing as sensible heat, and the other part being converted into mechanical work.
It matters not whence comes the heat, whether from the chemical transformations which take place in the body, or from the sun-force which has for ages lain locked in the coal-strata of the earth, when liberated or made dynamic, it represents a definite amount of mechanical power.
Nerve-energy is transformed into motion, as evidenced in muscular action; it is also transformed into heat, but it is not known whether it is an immediate or a secondary result. There are some instances recorded which seem to show its transformation into light, and it is well known that in certain animals electricity is the direct result of its metamorphosis.
From these data the conclusion seems authorized that at least a partial correlation exists between the physical forces and the energy resulting from nerve-action. I say a partial correlation, because, while the evidence may permit the conclusion that nerve-force is transformed into motion, heat, light, and electricity, it does not yet authorize the assertion that these can be reconverted into nerve-force.
This correlation doubtless extends to the higher manifestations of nerve-energy, feeling, and thought, for their exercise causes disintegration of nerve-tissue, as shown by the excreted products of decomposition and increased muscular action, as evidenced in the increased circulation of the blood. Physical conditions, therefore, determine mental results. The higher nerve-tissue of the brain operates under physical and chemical conditions in its nutrition, the same as does the tissue of any other organ, and hence its transformed energy, as expressed in nervous or mental action, has its physiological representation and measurable force.
To extend this subject further in the line of analysis, though it might be interesting, is unnecessary for the object proposed, which is to show that chemical, physical, and biological sciences have overthrown the vitalistic doctrines of the past, and demonstrated by analysis a relationship between the forces which rule the inorganic world and the "vital force" which is manifested in living forms. At this point the question is properly asked, if chemical synthesis confirms the results and conclusions of chemical analysis.
If the morphology and physiology of organisms are the products simply of physical molecules under chemical and physical forces which are revealed by analysis, then the assumption seems justified that synthesis, by combining these same molecules and restoring these same forces, should be able to reproduce the forms and functions of life.
Synthesis requires exact knowledge of all the elements and forces involved in the object of its investigation, and looks to the inductive or analytic method to furnish these data. There must be no unknown quantities in the problem to be solved, for synthesis seeks not to build from the unknown but only to re-form the known. Hence it properly awaits to receive verified facts from chemical analysis, which has yet been able to compass but a fractional part of the organic compounds.
Chemical elements are the basis of chemical science; they are neither produced nor destroyed, but are the enduring and constant factors in the many series of changes in the properties of matter, which represent the desideratum of this science. And yet the knowledge of molecules is very meager; the weights of but a few are known, even among the commonest elements and compounds; and but little account has been taken of atomic motion, which furnishes the most perfect explanation of chemical reaction.
Of the highly complex series of albuminoid substances, which neither crystallize nor possess any combining equivalent, and therefore can not be expressed by exact symbols, analytic chemistry knows but little, and hence it would be in vain to attempt their reproduction by synthesis. Notwithstanding our ignorance of essential facts, the progress of synthetic chemistry has been great, and the prospect is favorable for more brilliant achievements in the future.
Wöhler, in 1828, first, by synthesis, formed urea from ammonia cyanate. It was claimed by the critics that urea, being a nitrogenous metabolite, a product of animal decomposition, was a mineral, rather than an element of the animal tissues; but when Fownes, in 1841, prepared cyanogen itself direct from its elements, and, from this salt, urea, the fact was recognized and accepted, although it was affirmed that a "vital force" was necessary to account for the more complicated organic compounds, of which series urea was a member having only simple combinations. This was disproved by Berthelot in 1856, when he obtained the potassium salt of formic acid. Then followed the production of acetylene, marsh-gas, ethylene, and other hydrocarbons, from inorganic materials. Marsh-gas was converted into methyl alcohol, and ethylene into ethyl alcohol, and from these alcohols formic and acetic acids were made.
Startling as these results were, the substances formed were, relatively, simple in nature, and the "vital force" still ruled in the more complicated bodies of organic origin.
Synthetic work continued to achieve brilliant results and added to its list of vegetable compounds oxalic, valeric, malic, citric, tartaric, and salicylic acids, the oils of garlic, mustard, and wintergreen, also conine, alizarine, and indigo.
Of animal compounds, leucin, creatin, sarcosin, and taurin are added to the large and growing list of substances from which analysis and synthesis have banished the vital force, and harmonized the facts of their existence with the physical and chemical forces of the inorganic world.
Over one thousand organic compounds, which but a few years since were supposed to be formed within the vegetable or animal body only by the action of a "vital force," are now produced synthetically from the elements which constitute them, and "there is every reason to expect," says the conservative but able author of "The New Chemistry," Professor Cooke, "that in the no distant future the chemist will be able to prepare, in his laboratory, both the material of which the cell is fashioned and the various products with which it becomes filled during life."
It is true that the knowledge of man has not yet enabled him to make a vegetable or an animal cell, but this is no evidence in favor of a "vital force" per se, but an indication of ignorance relative to the ultimate constitution of the cell. Indeed, pseudo-organic forms, which resemble living cells, having heterogeneous contents, and true inclosing membranes possessing dialyzing power, have already been reported as produced by Monnier and Vogt.
It is well, however, to remind ourselves of the fact that the "cell," as commonly understood, embracing a cell-wall and an internal nucleus, represents in itself an advanced condition of organization, and not, as is so often inferred, the most primitive and simplest of life-forms. "Cell," in biology, "is a technical term used to denote a unit of living tissue," and the fact that the chemist can not make it is not proof that an independent life-principle resides in it, but is proof of ignorance of its organic formation.
If the fact of a "vital force," distinct from physical and chemical forces, is to be established because of inability to make by synthesis a living cell, then, in logical fairness, should this force, or some other equally independent of physical and chemical laws, be declared to preside over the genesis and potencies of those inorganic elements and bodies which thus far have defied, not synthesis only, but analysis also.
In germinal matter is found the apparent seat of life, for this it is that transforms pabulum to build the tissues at first, and in it lies the potency of restoring to physical completeness portions of the body that may be injured or diseased. The repair of living tissues after mutilation is not, however, positive evidence of the existence of a special principle, for the same action occurs in inorganic materials.
Pasteur records the fact that "when a crystal is broken on any one of its faces, and replaced in the fluid of crystallization, we remark that while the crystal increases in all directions by the deposit of crystalline particles, a very decided simultaneous action takes place at the broken or injured part, and this action suffices in a few hours, not merely for the general, regular formation of increase over all parts of the crystal, but also for the restoration of regularity in the injured part." Shall we ascribe a "vital principle" to the unorganized crystal as well as to the organized vegetable or animal tissue?
The mysteries of nature are not all confined to life-expressions. Who shall explain the ultimate nature of crystallization, which, under the laws of fixed axial ratios, gives to each variety such definite and invariable form? Who shall explain the flower's perfume? Where is the "vital force" in the seed which lies for ages in the tomb of some Pharaoh? Does "vital force," as an independent entity, which works contrary to physical and chemical laws, thus imprison itself and voluntarily submit to what must be, to it, a death? If it acts independently of the physical forces of nature, why has it not furnished evidence thereof in some way or at some time? How is life made active in this seed so long dried and practically dead? Not by any occult influence at discord with organic growth, but simply by environing the seed with conditions favorable to physical well-being. Heat, light, and moisture all physical and chemical agents soon revivify this seed, and evidence is added to sustain the proposition that, while "the present state of knowledge furnishes us with no link between the living and the not-living," yet are both actuated by forces of the same kind. "Vital force," therefore, is, in reality, only another term for the properties of matter; it denotes simply the causes of certain great groups of natural operations, as we employ the terms "electricity" and "electrical force" to denote others. But to use the term "vitality" or "vital force" in the sense of an entity, which acts as an efficient cause of vital phenomena, is an assumption as absurd as to assume that "'electric,' 'attractive,' and 'chemical' forces are entities which determine the phenomena of electricity, chemism, and gravitation."
"If we knew all the laws of the composition of matter, and all the changes of which it is capable, every phenomenon which any given substance presents must be caused either by something taking place in the substance or by something taking place out of it, but acting upon it. Those mysterious forces, whether they be emanations from matter or whether they be merely properties of matter, must, in an ultimate analysis, depend either on the internal arrangement or on the external locality of their physical antecedents. However convenient, therefore, it may be, in the present state of our knowledge, to speak of vital principles, imponderable fluids, and elastic ethers, such terms can only be provisional, and are to be considered as mere names for that residue of unexplained facts which it will be the business of future ages to bring under generalizations wide enough to cover and include the whole."
As mechanical energy manifests different powers and results as it operates through differently constructed mechanisms, so vital energy becomes more complex in its manifestations as the organism through which its work is displayed is more complicated in structure.
Jevons has well defined the physiological significance of "vital force" thus: "We are at freedom to imagine the existence of a new-agent, and to give it an appropriate name, provided there are phenomena incapable of explanation from known causes. We may speak of vital force as occasioning life, provided that we do not take it to be more than a name for an undefined something giving rise to inexplicable facts, just as the French chemists called iodine the substance x, so long as they were unaware of its real character and place in chemistry. Encke was quite justified in speaking of the resisting medium in space so long as the retardation of his comet could not be otherwise accounted for.
"But such hypotheses will do much harm whenever they divert us from attempts to reconcile the facts with known laws, or when they lead us to mix up discrete things.
"Because we speak of vital force we must not assume that it is a really existing physical force like electricity. We do not know what it is; we have no right to confuse Encke's supposed resisting medium with the bases of light without distinct evidence of identity. The name protoplasm, now so familiarly used by physiologists, is doubtless legitimate so long as we do not mix up different substances under it, or imagine that the name gives us any knowledge of the obscure origin of life. To name a substance protoplasm no more explains the infinite variety of forms of life which spring out of the substance than does the vital force which may be supposed to reside in the protoplasm. Both expressions are mere names for an inexplicable series of causes which, out of apparently similar conditions, produce the most diverse results."