Life in Motion/Lecture I

by John Gray McKendrick

LECTURE I
Introduction—Movement in general—Molecular movements— Muscles—Organ and function—Muscular contraction.

The object of the courses of Christmas lectures at the Royal Institution is to interest the young in the principles and the progress of science. This has been many times successfully accomplished by describing in simple language and, if possible, by demonstrating, the laws that govern a well-known phenomenon, such as the burning of a candle or the formation of a soap-bubble. The study of these familiar things is the door by which we may enter into the domain of natural philosophy. As described by Faraday, a candle-flame became a centre around which we found clustered the fundamental facts and principles of chemical, and even of physical science; and the consideration of a soap-bubble (as in the lectures in this place by Professor Dewar two years ago), its production, form, colour, is worthy of the intellect of the most profound philosopher, while it is an unfailing source of amusement and instruction to the youthful mind.

But, my young friends,—and it is to you I shall address myself in these lectures, although I am glad to see so many present who are older in years, but who can still relish a simple lecture to juveniles,—there is another department of nature that is not, strictly speaking, the province of the natural philosopher. There are the phenomena of living matter, the events that happen in the life-history of living beings, the changes that occur in our own bodies, and on which our lives depend. These are investigated by the physiologist; and we shall find, as we go on, that they are not so easily demonstrated as many of the phenomena that happen in dead matter, and that they are, on the whole, more difficult to understand. Following, however, the example of previous lecturers, I have endeavoured to choose a subject, the consideration of which will form an introduction to physiology, which will illustrate how physiologists work in their laboratories, and how they reason about the problems they have to solve.

I have called the subject of the course "Life in Motion." We must take care at the outset not to outset into difficulties about what is implied by the word Life. We shall not inquire, in the meantime at all events, whether life may be considered as something independent of matter, or whether it is the outcome of material arrangements. It will be better at first to use the words Living Matter instead of the word Life, and to define our subject of study as Living Matter in Motion, or the Motions of Living Matter. We might study other aspects of living matter, as, for example, the chemical changes occurring in it, the forms it assumes, its arrangements for different purposes, or its wonderful connection in some conditions, as in the brain, with consciousness. We shall, however, limit ourselves to the consideration of its motions; and we shall refer to the other properties of living matter only in so far as these throw light on the secret mechanism by which it moves.

We are familiar with motion every day of our lives. We know, first of all, of great movements of matter, such as the wheeling of the planets in their elliptical orbits round the sun, the spinning of the earth on its axis, or the still grander movements of the firmament, as revealed by the proper motions of the stars. Such movements impress the imagination with a sense of vastness and of irresistible power. Then there are the movements on the surface of the world itself—the tides, the flow of rivers, the hurricane, the clouds travelling athwart the sky, and many others. These are movements of great masses of matter; and when they are studied by the natural philosopher, he finds that they are regulated by well-known dynamical laws. All such movements are evident to the senses; but there are other movements that are not so, and which can be detected only by special methods of research. Such are those that occur, as it were, below the surfaces of things. These are called molecular, because the bodies that move are minute particles or molecules of matter, far too small to be seen with the eye or even with the aid of the most powerful microscope. Still, the natural philosopher tells us that the movements of these little particles are controlled by dynamic laws as definite in their operation as those that govern the planets in their journeys round the sun. The physicist, however, deals with another and more subtile class of movements in an Ether, which he supposes to pervade space. Waves, strains, pressures, whirls in the ether, account to men of science for many of the facts of heat, light, and electricity. Thus, according to the scientific conceptions of the present day, we have to imagine all the matter in the universe as in a state of movement, some movements large and occurring in vast stretches of space, and others almost inconceivably minute. Nothing in this vast mechanism has come to rest. Each particle of matter is quivering, molecules of all gases are vibrating to and fro, and millions of wavelets are streaming through the ether in all conceivable directions. If we suppose that the essence of life is movement, does not this give one a conception that in a sense the universe is alive?

We have to deal, however, in these lectures with the movements occurring in living matter. We all know that the living things with which we are familiar move. They move their bodies as a whole, or they move parts of their bodies. Animals run, leap, swim, fly, and perform many other movements. These movements are obvious. Every one can see them. But here, again, we must go a little farther in thought and look below the surface. We then find that in living things there are also molecular movements, and that the larger movements which we can all see depend on the small ones that are invisible to our eyes.

To aid us in understanding these statements a little better let us now perform a few experiments. Take, first of all, one or two chemical reactions. I add a solution of nitrate of silver to a solution of chloride of sodium. You see a solid matter appear, which soon falls to the bottom of the glass. This solid matter is chloride of silver, a new substance formed by the interaction of the nitrate of silver with the chloride of sodium. The change may be expressed in this way:—

Nitrate of Silver	$+$	Chloride of Sodium
$\scriptstyle {\underbrace {\quad \quad \quad \quad \quad } }$		$\scriptstyle {\underbrace {\quad \quad \quad \quad \quad } }$
consists of Nitric Acid and Silver		consists of Chlorine and Sodium
	gives
Chloride of Silver	and	Nitrate of Soda
$\scriptstyle {\underbrace {\quad \quad \quad \quad \quad } }$		$\scriptstyle {\underbrace {\quad \quad \quad \quad \quad } }$
Chlorine and Silver.		Nitric acid and Sodium.

In other words, both substances—nitrate of silver and chloride of sodium—were split up into their constituents, and the molecules of chlorine, forsaking the sodium, travelled to and united with the molecules of silver to form a new substance called chloride of silver. Again, if I add a solution of iodide of potassium to a solution of corrosive sublimate, we get a beautiful coloured substance called iodide of mercury. A new substance has been formed by the iodine and potassium parting company, the iodine then uniting with the mercury of the corrosive sublimate to form the salt called iodide of mercury, while the potassium united with the chlorine to form a substance known as chloride of potassium. We may picture the molecules of these substances, at the moment of chemical change, rushing from one to another so as to form new combinations.

Look at what is going on in this large glass vessel. A few hours ago I placed in the vessel a solution of grape sugar, and I added a small quantity of fresh yeast. The fluid was at first clear, now you observe it is turbid and is yellow in colour. Notice also the froth gathering on the surface. Fermentation is going on actively in the fluid. Gas is passing off in large quantities. Under the action of the minute living vegetable cells that constitute yeast, the sugar is being split up into alcohol and carbonic acid. The alcohol remains in the fluid and the carbonic acid escapes into the air. Observe when I put this lighted taper into the vessel that the flame is at once extinguished Fig. 1.—Yeast cells. The cells of Saccharomyctes cerevisiæ, multiplying by budding. Magnified 300 diameters. by the carbonic acid gas. Here we have an example of molecular movements brought about by the action of living organisms—the yeast cells. Each little yeast cell acts directly or indirectly on the sugar, effects a decomposition, as I have said, into alcohol and carbonic acid, while other substances, such as glycerine and succinic acid, are formed in smaller quantity. During the fermentative process the temperature of the fluid rises, and the yeast cells grow and multiply, living, as it were, on the sugar and other nutritive matters in the fluid.

Let us pass to another experiment. I have prepared a saturated solution of acetate of sodium—that is, a solution which cannot be made stronger. You observe it is a clear fluid like water. I now drop in a crystal of acetate of sodium. You see at once crystals shooting through the fluid, and in a few moments the mass in the flask has become solid. The flask has also become perceptibly hotter. The agitation excited by dropping in the crystal has caused a rapid change in the position of the particles, the solution passing from the fluid to the solid state with the evolution of heat. This is another example of a molecular movement.

Consider next an experiment in which a state of movement can be appreciated by the eye. Look at the limbs of this large tuning-fork. You observe they are stationary. I strike the fork, and you see it is at once thrown into a state of vibration, as shown by the fuzzy appearance of the limbs when placed in the electric beam. Listen, and you hear a low, humming sound. This is caused by the movements of the fork sending a number of pulsations through the air, which strike against and agitate the drum-head of the ear, and from it the movements are communicated to the Fig. 2.—Movements of limbs of tuning-fork. A, limbs at rest; B, in movement. nervous structures in the deeper ear. If I touch the limb of the fork with my finger, the fuzziness vanishes, the image now appearing sharply on the screen, and the sound is no longer heard. I shall next cause this smaller fork to sound by drawing a fiddle bow across one of its prongs. You hear it sounding. I place it in the electric beam. You see the shadow of its limbs are well defined on the screen. You cannot see its movements, as you saw the movements of the first fork, because they are too fast for the eye. But they are not too fast for the ear, because we hear the sound; and they are not too fast for the sense of touch, because when I touch the fork I feel a thrill against my fingers. The pressure of my finger stops the vibrations and we no longer hear the sound. The large fork vibrated 128 times in each second, and the smaller one moved twelve times as fast, or 1536 times a second.

I strike with a key a little cylinder of steel suspended on this support. You hear the sound, but I need hardly point out you cannot see the movements of the cylinder, nor do I feel a thrill when I touch it. The movements, occurring about 12,000 times a second, are too fast for the eye and too fast for touch, but they can still be followed by the ear. Lastly, I strike this smaller cylinder. You hear the dull thud of the stroke, but no piercing tone is heard; and yet this cylinder is no doubt vibrating, but its movements are too fast to be followed by any of the senses. Thus we learn that our senses are limited organs as regards the detection of movement. We can only follow periodic movements through a narrow Fig. 3.—steel cylinders emitting a high tone when struck, a, 12,000 vibrations, b, 20,000 vibrations, and c, 30,000 vibrations per second. range; and there are regions in which delicate movements occur, which we can only explore by indirect methods and by processes of thought.

Let me point out to you, in passing, that man's supremacy over the lower animals lies in the power he possesses of pushing his inquiries far beyond the range of his senses. From facts that appeal to his senses he reasons as to phenomena that can never be directly observed, and by intellectual processes he can acquire knowledge as accurate as if he were able to examine the phenomena with organs of sense having powers much more extensive than those he possesses. A recognition of this quality of man's mind indicates also the value of education in science. This does not consist, as is often erroneously supposed, in merely acquiring a knowledge of fact, but also and more in learning to reason correctly and in cultivating the use of the imagination. The scientific thinker has a mental vision into regions far beyond the limited powers of his senses, and hence there is much truth in the statement that the greatest scientific men have many of the qualities of mind of the poet or of the prophet. They are seers in a true sense of the word.

Let us take another simple experiment or two from the region of physics, to prepare the way for our own special study. Here is a mass of soft iron, like the half of a link of a large chain. Copper wire has been coiled round each limb, and we can connect the ends of the copper wire with an electric battery. If I take into my hands the ends of the wires coming from the battery, I feel nothing, so that any force that may be coming from the battery is not

Fig. 4.—Electro-magnet supporting a weight, a, stand; b, galvanic element; c, key; d, electro-magnet; e, keeper ; f, weight.

affecting my skin so as to cause any kind of sensation; but if I touch the tip of my tongue with the wires, I have a peculiar sensation of taste. The tongue tells me that something is affecting me, although the hands are apparently not influenced. Still we know that chemical changes are going on in this battery, and that these changes are followed by something we call a current of electricity. The best proof of this I can give you is that if I send this current round the wire covering the ends of the link of soft iron, you will find the properties of the soft iron altered so that it becomes powerfully magnetic. You observe that when no current is flowing, as is the case when I break the connection, the soft iron has no attractive influence on this piece of steel; but when I send the current on, at once the soft iron becomes so powerfully magnetic that it attracts the steel keeper with great force—a force so great that you see the keeper supporting a heavy weight. A wonderful change has been wrought in the soft iron—a change depending on molecular movements far too fine to come within the range of direct observation. It can be shown, however, that such a piece of soft iron actually elongates when the current passes round it, as in this experiment; and if I were to interrupt this current so as to send it at short intervals of time, the mass of soft iron would vibrate so as to give out a musical tone. It is not in my province to discuss these remarkable physical Fig. 5.—Muscles in human arm. b, biceps muscle. phenomena; but I ask you to remember this simple and familiar experiment, because it not only is an example of what we mean by molecular movement, but it explains the construction of many physiological appliances we shall use in future lectures. Now we come to movements associated with life. These are best studied in a muscle. Flex your arm at the elbow joint, and you will feel the flesh above the joint and in front of the arm become firm and hard. Extend the arm and it again becomes soft. These movements are made by the action of special organs we call muscles; and the particular muscle I ask you to notice in the arm is called the biceps. Every boy knows where his biceps muscle is, and when he is training for throwing the cricket ball, or for rowing, he feels his stiff and firm biceps with a certain amount of commendable pride. A young lady has a biceps also;

Fig. 6.—Muscles of frog's leg. g, c, the gastrocnemius muscle often used in physiological experiments.

but she is not so much interested in its welfare. In a section of a limb, such as you find at any butcher's stall, you see the masses of red flesh imbedded in fat and loose tissue. These masses of red flesh are the muscles. But if we dissect a limb, we find that the muscles are beautiful organs, adapted, as regards form and length and bulk, to the work each has to perform. This diagram will give you a conception of what we mean by a muscle. It shows the muscles of a frog's leg. You observe that, as a rule, a muscle springs from a bone, and is attached at the other end to another bone, a joint, sometimes two or more joints, intervening. One end of such a muscle as the gastrocnemius (Fig. 6) muscle terminates in what is called a tendon or sinew—a fibrous structure which is attached to a membrane covering the bone. The muscles are the living ropes that pull the parts of the animal machine.

We may call the muscles the organs of movement. By an organ physiologists mean a part of the body devoted to a special use or purpose, or, as we say, a function. A muscle has its own work to do, in a sense as true as that the heart has its own work to do in acting as a force-pump to drive on the blood through the blood-vessels, or, in other words, to keep up the circulation. It is important to notice that a muscle may be regarded as an independent living thing, an organ that in certain conditions might live and work by itself. It has its own blood-vessels for supplying it with nourishment, its own nerves for stimulating it to activity, or for putting it into relation with the headquarters in the nervous system, and its own arrangements for the removal of so-called waste matters that have arisen from the tear and wear of the muscle in its active life.

Now, suppose we could isolate a muscle from the rest of the body and keep it alive, you can see that we might be able to examine the changes that occur in it when it works. So long as it is in the body, we cannot easily subject it to the method of experimental inquiry, because it is, in the first place, part of a living sentient being; and, in the next place, it is part of a complicated organism, the functions of which are all so closely connected, that if we interfere with the mechanism of one part we interfere with the whole, and this disturbance of the functions of the body as a whole reacts upon the functions of the very part we desire to study. Obviously, then, our course is to remove the muscle from the body and to keep it alive. But we are met by the difficulty that if we do so the muscle will soon die. Here you see at once one of the serious disadvantages at which the physiologist is placed in the prosecution of his science. The things the natural philosopher deals with are dead things. He can isolate them and interrogate them at pleasure by experiment, submitting them to all sorts of conditions and changes of circumstances, without the risk of destroying them or even of altering the property he wishes to examine. Many of the phenomena he has to investigate are of a tolerably permanent character, and the things he operates upon are, as a rule, not the seat of constant change. I admit that this is only generally true, and that there are phenomena sometimes investigated by the physicist which are almost, if not quite, as brief and evanescent as those that come under the eye of the physiologist. Still the statement is true in the main.

The things the physiologist has to investigate only work within a narrow range of conditions. Alter the blood supply, allow drying to take place, change the temperature, and the phenomenon he is in search of cannot be found. Modify the conditions of life beyond certain limits, and death at once begins. In trying to find out what are the phenomena of life we arrest the very phenomena we are in search of. Thus we kill the goose that lays the golden eggs.

Look at this piece of clockwork. Suppose I saw it for the first time and desired to know how it worked. I could do so by watching the movements, observing the slow uncoiling of the chain, and the movements of pinion and toothed wheel. I might also take it to pieces and study the various parts. By taking it to pieces the mechanism no doubt would stop, but I might, by careful consideration of how one thing fitted into another, ascertain how the thing worked.

The body may be regarded as an extremely complex machine, intimately connected in all its parts, but yet it is possible to make out, by direct inspection, something about the uses of its individual parts. We can see that the skeleton forms a scaffolding for the soft parts of the body, that the muscles and joints form a system of levers by which movements are effected, that the heart pumps the blood, and that the lungs are used for breathing. We can stop the machine and study the form and structure of the various parts. This is the province of the anatomist. Further, as I have said, we can watch the machine in action. This is the work of the physiologist. But the peculiarity of the physiologist's machine is that each part of the mechanism is alive. Each individual organ is a machine or instrument by itself, and its use as a part of the whole complex machine depends on the molecular machinery which composes the individual organ. Returning to the analogy of the watch, it is as if each wheel, and pinion, and chain were a separate machine, more complex, perhaps, in structure than the watch itself. It is as if we had wheels within wheels, and as if the mechanism depended partly on the large wheels, and partly and mainly on the small wheels within the large ones.

In like manner our study of muscle must include the action of the muscle as a part of the body, and also the changes that happen in the muscle itself, and by which it works. We shall take the last part of the investigation first, and we shall therefore try to find out what a muscle does and how it works. Let us interrogate a muscle itself. I have prepared the muscle of a frog in the way shown in this diagram. Now I wish you to follow all I do; and you must receive all the explanations that I would think it necessary to make Fig. 7.—The gastrocnemius muscle of a frog prepared for experiment. F, femur, bone of the leg; N, sciatic nerve ending in muscle at n; J, tendon of Achilles, with a small hole in it for a hook. if you were beside me in my laboratory. How has the muscle been prepared? As you know, the frog is what is usually called a cold-blooded animal, that is to say, the temperature of the body is always not far from that of the medium in which it lives. The term "cold-blooded" is misleading, because the frog's blood may, in some circumstances, not be cold; and besides it is a term to which one would think the frog might take just exception as being a term to which an evil meaning has been attached, as when we speak of a cold-blooded villain! The term "variable temperature" is more correct, as it distinguishes all such animals from those in which the blood has an almost uniform temperature, whatever may be the temperature of the medium in which the animal lives. For example, the temperature of a healthy man in the buruing plains of India or in the snowy wastes of Siberia never varies much from 98.4° Fahrenheit.

It is one of the characteristics of animals of variable temperature, like the frog, that all its tissues are more stable or permanent than those of animals of uniform temperature. The tissues of a frog are not so liable to change as those of a rabbit or of a bird. Now the active phenomena of life all depend on instability of tissue. Imagine you have built a house of cards. You might build it so that the slightest push, or even a whiff of air, might cause it to fall to pieces; or you might so construct it that considerable force would be needed to knock it down. In the first case, the house of cards would be unstable; in the second, it would be stable. The tissues from the two kinds of animals differ in a similar way. When the death of the animal occurs, when breathing ceases and the blood stops flowing, in the case of an animal of uniform temperature the unstable tissues at once begin to change, and they speedily lose their vital properties and die. On the other hand, in similar circumstances, the more stable tissues of an animal of variable temperature undergo but little chance for a considerable time. Thus it is that the tissues of a frog live much longer after the death of the animal than those of a rabbit, or of a rat, or of a man. The muscles live after the death of the animal. As an individual, the frog is dead. It died instantaneously and without pain, but its muscles still live, and, in suitable conditions, they may live for hours. Thus you see that the mysterious property we call life (if you choose to call it a property) is not in one part of the body more than in another, but is diffused through it. We have stopped the watch, but bits of the mechanism are still going on. By and by they will stop also, and then there will be complete death.

Now look at our preparation (see Fig. 7 p. 23). You see the muscle—the gastroenemius we call it—attached to the lower end of the thigh-bone or femur. The other end terminates in a tendon—the tendon of Achilles—fixed to the heel of the foot. It is the same muscle as forms the calf of the leg in our own bodies, and the tendon is the firm band you can feel above the heel. Observe the whitish thread passing into the preparation. This is the sciatic nerve, a great nerve that runs down the back of the thigh, sending branches into the gastrocnemius and to other muscles. I shall now clamp the upper end of the femur or thigh-bone by these forceps and pass a little

Fig. 8.—Platinum wires, a and b, with nerve, n, stretched across them.

hook through the tendon. This hook is attached to a silk thread connected with this instrument, which we may call a muscle telegraphy, and by which any movement of the muscle will be made visible to US. Then we stretch the curve accros two little platinum wires coming from an electric arrangement which I shall not at present explain (Fig. 8). We will not use the telegraph, as the signal may not be easily seen, but we will cause the muscle when it contracts to ring a little bell. Here you see the shadow of the apparatus cast on the screen by the electric light. I intend to use electricity to stimulate or irritate the nerve or the muscle at pleasure, and I have so arranged the apparatus that I Fig. 9.—Arrangement of apparatus for irritating the muscle, g, directly, or the nerve connected with it at f. a, galvanic element; b, key; c, primary coil of induction machine; d, secondary coil; e, commutator by which current can be sent either to nerve or to muscle; f, electrodes, as in Fig. 8, for the nerve; g, muscle; h, small hammer; i, weight. can send a single shock to the nerve or muscle, or a number of shocks in quick succession. We have now got everything adjusted. Observe that when I send a shock to the nerve the muscle gives a twitch and pulls on the thread, and observe the little hammer striking; the bell. The muscle has contracted only for an instant and you hear one stroke of the bell. Another shock causes another twitch; and we find that if we allow some time to elapse between successive shocks, there is a twitch with each shock. But the twitch is so Fig. 10.—An enlarged view of the muscle-bell, a, thread coming from tendon of muscle; c, thread for weight; b, hammer for the bell g. fast, it occurs in so short a time, that the eye can scarcely follow it, so that we cannot see what the muscle really does. But I now send a rapid series of shocks, and you observe that the muscle has become shorter and thicker. It has also pulled on the thread of the telegraph, and the hammer of the bell is kept up. This condition you will notice is not a rapid, sudden twitch, but a slow, steady, persistent pull or contraction. The muscle has passed into a state of cramp, or, as physiologists term it, a state of tetanus. The short, sudden contraction we shall call a twitch or simple spasm.

We repeat the experiment, only irritating the muscle instead of the nerve, and we get the same result: a single twitch with a single shock and tetanus when the shocks come in rapid succession.

We have learned from this experiment, then (1), that when we irritate the nerve going to a muscle, the muscle becomes shorter and thicker, or, in other words, it contracts; (2), that a single shock of electricity to the nerve is followed by a sudden sharp twitch, a single contraction; and (3) that a number of shocks sent in rapid succession to the nerve causes the muscle to pass into a more lasting state of contraction called tetanus or cramp.

In the experiment we have just performed all the work the muscle did was to pull up the signal and ring the bell. It does not require much energy to do this, and the experiment gives one a very inadequate notion of the amount of energy that can be brought into play by a small muscle like the one we are now studying. Here is another muscle of the same size. It weighs about half a gramme, or about seven grains. We have suspended it so that Fig. 11.—Arrangement of apparatus for showing muscle lifting a weight, b, galvanic element; b (in middle), electric bell; p primary and s secondary coil of induction machine; a, frog interrupter; m, muscle. See next figure. when it contracts it lifts a lever, and, breaking an electric circuit, causes a bell to ring. This apparatus, I may mention, was sent to me for these lectures by Professor du Bois Reymond of Berlin, who lectured on "Nerve and Muscle" in this Institution in 1855, and who has taken a warm interest in the success of the present course. I put a weight on the scale-pan below the lever and irritate the muscle. Observe it can lift, as you hear by the tone of the bell, 5, 10, 20, 30, 40, 50, 100, 200, 250, 300, 350, 400, even up to 500 grammes. It can Fig. 12.—Essential part of frog interrupter used in experiment represented in Fig. 11. m, muscle; n, nerve; c, lever; when c is raised by the contracting muscle m, the contacts at x and y are broken; x is a platinum where dipping into mercury, and y is a contact between two platinised surfaces. The arrows near the wires connecting x y show direction of current. When contact is broken by lifting the lever c, the bell b (middle) in Fig. 11 rings. actually, by a sheer pull, move a mass one thousand times its own weight. Is not this a wonderful expenditure of mechanical energy?

The obvious phenomenon of a muscle, then, is that it contracts or changes its shape when it is irritated. We say that a muscle, like other living matter, is irritable. By this we mean that it responds to a stimulus, and the response is a change of form, a contraction. We shall see, however, that the contraction or change of shape is associated with many other changes of a molecular character not obvious to the senses but to be looked for by special methods. We must also, in next lecture, study more carefully the contraction itself.