John Gray McKendrick

“ 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. ”

“ It expends or produces mechanical energy, and it also becomes hot. But we know that energy never comes out of nothing. You cannot get it for nothing. You can only get it by the expenditure, or, if you put it in another form, by the disappearance, of another mode of energy. This is one of the greatest thoughts of modern times—this thought of the persistence of energy. We cannot create or destroy matter. We can only transform it. In like manner, we cannot create or destroy energy. We can only transform it. Our steam-engines, and gas-engines, and hot-air engines are all transformers of energy. ”

“ 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. ”

“ This is another example of how valuable to humanity the frog has been in the way of giving scientific information. It is not too much to say that each time your physician sees you when you are ill he brings to the study of your case knowledge that has been gathered for him by the physiologist from the frog. As we are in the habit of commemorating by monuments the services of those who have been benefactors to humanity, I know no animal,—no tiger, lion, or panther,—that better deserves a bronze statue than the humble frog. ”

“ Our arrangements for studying muscle are not yet complete. We have already seen that a muscular contraction is so rapid as to make it impossible to follow all its phases with the unaided eye. The questions at once occur to us: how long a time does it take to contract? if it does not contract at the same rate throughout its contraction, for how long a time does it contract quickly, and for how long a time does it contract more slowly? ”

“ This shows that when the little machine cannot give its output of energy at the expense of carbo-hydrate or of fat, it sacrifices a part of its own framework. The muscle engineer, when he finds himself short of the ordinary fuel, seizes hold of combustible portions of his own engine, as if he were determined at all costs to do the work required of him. This is only a somewhat fanciful analogy, but it gives us an insight into what probably occurs in a muscle.
An engineer is desirous, chiefly for the sake of economy, to get as much effective work as possible out of the engine he constructs. ”

“ But the constituents in the food stuffs are not quite the same as those in muscle, and they are therefore subjected to many chemical processes in digestion by which they are first converted into stuffs that exist in the blood. From these stuffs in the blood the muscle builds up its- substance. Now all of these stuffs, from the scientific point of view, contain energy in what is spoken of as a potential state, that is to say, it is resting, ready to be set free, ready to do work, and when it is set free it may become, as it does become in the case of the muscle, mechanical energy and heat. ”

“ It is evident, therefore, that, considered as an engine, a muscle is not much better as a transformer of energy than the best steam-engine now constructed, while it is inferior to certain gas-engines which are said to return as much as twenty per cent in the form of effective mechanical energy. The muscle, however, has this great advantage over any engine, that the heat it produces supplies one of the conditions of its very existence, the maintenance of a certain uniform temperature. ”

“ In the body, the muscles are always partially on the stretch. They are never "on the slack," to use a familiar phrase, and they are ready to exert a pull on the bones to which they are attached, the instant they begin to contract. Thus no power is wasted. Further, as has been ingeniously shown by Professor Marey, the elasticity breaks the force of the shock produced by the sudden contraction of the muscle, and the energy of the contraction is expended more gradually and effectively than if the muscle had been non-elastic. ”

“ Electrical phenomena of muscle—Current of resting muscle —Current of acting muscle—Negative variation—Animal electricity—Electric fishes—Resemblance of electric organ to muscle—Relation of muscular motion to nervous system—Conclusion.
To-day I wish, in the first place, to demonstrate to you certain properties of muscle to which I have not alluded. I will show you that muscle has electrical properties. Let us examine some of the facts that led to the discovery of animal electricity, a discovery of the most momentous consequences to the human race. ”

“ 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. ”

“ We often, however, fall into the bad habit of allowing our muscles to be inactive, and the result is they become weak and attenuated. Exercise is needed. Run the machinery and you obtain the wonderful result that the living machine improves in strength and size. The mere act of making the muscle work develops its powers. It grows stronger and thicker, and it works with greater precision and effectiveness. Hence the value of athletic exercises, if carefully carried out. They should not, however, fall on one muscle or one set of muscles exclusively. ”

“ Butter is a mixture of various fats, and as fats are soluble in ether, it is easy to make an ethereal solution of the fat of milk by shaking up milk with ether, after adding a little caustic potash to it and keeping it moderately warm. In this long tube you see a layer of ether holding fat in solution, floating on the top of the fluid. Fat also consists of carbon, hydrogen, and oxygen, but in proportions different from those in which these elements exist in the carbo-hydrates. It contains no nitrogen. Fatty matter must always exist in a diet suitable for sustaining life. ”

“ 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 have now seen how nerves and muscles may be irritated in a definite and precise way, and we have found that the irritation of its nerve causes a contraction of a muscle. In the case of a single twitch, however, the movement is too rapid to be appreciated, and still less analysed, by the unaided eye. We cannot tell, for example, whether the contraction occurs in a shorter time than the relaxation, and still less whether the contraction is at a uniform rate in time, or whether it contracts faster at the beginning and more slowly towards the end, or the reverse. ”

“ It is not so easy to show that even a simple contraction produces heat, because such a movement of the gastrocnemius of a frog is associated only with a rise of temperature of from one-thousandth to onefive-thousandth of a degree centigrade. Tetanus of frog's muscle gives from fourteen to eighteen-thousandths of a degree centigrade. No doubt each contraction of the muscles of higher animals, such as those of man, produces or is associated with more heat, but still the amount for each individual contraction is not much. ”

“ To start a mechanism that will produce well-ordered movement, as when I lift this book from the table, impulses or messages, whatever you like to call them, must first be transmitted from the body itself to the brain. Such messages may come to the brain by nerve-fibres from some organ of sense, it may be from the skin, or from the eyes, or from the muscles themselves, but they must be sent to the brain before the brain will send out messages along motor nerves to groups of muscles which are called into action, so as to perform a definite movement. ”

“ It is not a heat-producing machine. The primary function of a muscle is to contract, and thus to do effective work; but by producing heat at the same time it becomes possible for the muscle -substance to do its work in the best possible conditions. This is only another illustration of that wise economy that we see in most, if not in all, of the arrangements of nature.
After considering the points discussed in this lecture, you will readily understand how it is that a muscle becomes tired. It becomes fatigued after continuous work. Fatigue means a diminished power of work. ”

“ 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. ”

“ Science, then, demands the accurate measurement of time, and no small fraction of time is too insignificant to be of importance. The twentieth, the hundredth, the thousandth of a second is to science as precious as an hour may be to many people. It may be said without irreverence that to science a day is as a thousand years, and a thousand years as one day. The methods of science for this purpose are founded on two sets of appliances: first, the use of instruments, like a tuning-fork, that are found to vibrate or move at a known rate, say one hundred or five hundred times per second ”

“ 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. ”

“ When the nerve-current reaches the muscle, it sets up molecular changes in it, and these changes are expressed to our eyes by a contraction, heat at the same time being liberated. The electric current we call a stimulus. We use electricity for stimulating the nerve because it is a convenient method, but the nerve, as we shall see, might be stimulated in other ways, as by mechanical irritation, such as pricking, pinching, or beating, or by heating it suddenly. It does not matter, however, how we stimulate the nerve ”

“ Science is simply the truth about natural phenomena, so far as we can reach it. Some of you may become men of science, and you will probably advance much farther than we can do at present, and you will add to science, I hope, by your own work. The majority, however, will not follow scientific pursuits, but I trust this course of lectures will lead you always to keep a mind open for the reception of truth, from whatever quarter it may come, and that you will always cherish a lively sympathy with scientific men and with scientific progress. ”

“ At least a part of the carbonic acid is the waste product arising from the decomposition of the carbo-hydrate.
Now if the muscle receives no carbo-hydrate, or an inadequate supply of it, it does not follow that it will stop working. Experiment has shown the contrary. It will still work, using up the fat in the first instance; and if there is an inadequate supply of fat, it actually uses up proteid matter, or, in other words, it uses its own substance. If an animal is caused to work very hard, we do not find an increase in the excretion of the nitrogenous waste matters, as Liebig supposed ”

“ In the latent period, the muscle is preparing for making the movement. Very refined methods show that the latent period is shorter than the one-hundredth part of a second. Professor Burdon Sanderson has found, by a photographic method, not so liable to experimental errors as the one I have shown you, that in the muscles of the frog it is about the one-two-hundredth part of a second. Probably it is even shorter in the muscles of the higher animals. Their muscular substance is more unstable than that of a frog, and it goes off more rapidly under the nervous stimulus. ”

“ A contracted muscle, according to this view, is like a strong band of india-rubber pulling on two pieces of wood and drawing them together. In like manner, when a muscle contracts, a similar elastic power is developed that pulls upon the bones and causes movement. When the contraction ceases, the muscle returns to its original length, again by elasticity, but acting in the opposite way.
What is this property of irritability by virtue of which the muscle responds to a stimulus and contracts? ”

“ It is always engaged in mending itself, building up so as to make good the waste, and in this way for a long time it is able to work efficiently. The substances needed for building it up are brought to its own door by the blood, many of them ready made, and it takes them into itself and repairs the machinery. These substances for repair are no doubt the proteids, the carbo-hydrates, the fats, saline matters, and water. They all seem to be necessary for the upkeep of the muscle-substance. ”

“ 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 ”

“ The current of the cut muscle at rest is not of so much importance as the current of the same muscle in action. There are strong reasons for holding that the resting current is due to the death or dying of the layer of muscle-substance laid bare by the transverse section. Dying muscle-substance, it would appear, becomes negative to living substance. But the negative variation current, or the action current, as we may well term it, indicates changes happening in the muscle, changes that are somehow connected with the phenomena of contraction. ”