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'The vegetable organism is a machine in which the sun's energy is absorbed in the pulling apart of carbon and hydrogen from oxyThe light and heat force emanating from

gen.

the sun is rendered latent in the separated oxygen and hydro-carbon, just as human muscular force is rendered latent in the stretched cross-bow. When the separated hydro-carbon, in the form of some vegetable product, is recombined with the evolved oxygen, as in burning coal or wood upon the fire, or in consuming bread and oil and wine in the animal frame, the heat liberated in both instances is nothing more than the heat of the sun which had been stored up in carbo-hydrate and oxygen respectively. Conversely, the animal frame is a machine in which the sun's energy is set free by the recombination of that oxygen and carbo-hydrates, in the pulling apart of which it had been absorbed or rendered latent.

The plant may be regarded as a miser or hoarder up; the animal, on the other hand, as a spendthrift or dissipator of the sun's force; but just as the miser is not a producer, or the spendthrift a destroyer of gold, so neither is the vegetable a producer, nor the animal a destroyer, of force. All modern philosophy combines to prove that force, like matter, is indestructible. It may be accumulated, but not created; dissipated but not destroyed.-P. 76. All alimentary substances may be divided into two great classes. The first class contains albumen, fibrin, casein, and their modifications, and are found equally in plants and in animals. These substances are distinguished by containing about fifteen per cent. of nitrogen, or just the same amount as dried flesh and blood, from the composition of which they do not materially differ. Hence Liebig has called them the plastic elements of nutrition;' the name has been shortened in this country into the more convenient term of 'flesh-formers.' According as these are more or less present in food, so is that food, if other nutritive conditions be not wanting, more fitted for building up the fabric of the body. Lean meat consists almost wholly of these flesh-formers, among which fibrin is predominant. The white of an egg offers them in the form of albumen, as the curd of cheese does in that of casein. But they are not confined to substances of animal origin, for the fibrin abounding in beef is largely found in wheat flour; the albumen of the egg may be extracted from cabbages; and the casein of milk is present in still larger quantity in beans and peas. All of them are originally derived from plants, for animals seek them out from the vegetable food which they consume, and merely deposit them upon their bodies. Nor do the carnivora form an exception to this law of nutrition, as they feed on herbivora, which yield to them the materials for their flesh. The process of animal nutriN-12

VOL. XLV.

tion, so far as building up the body is concerned, is remarkable in its simplicity. Plants, having no high functions of volition life, and prepare the materials of flesh and to perform, become the laboratory of animal blood. Animals merely extract these, and give to them a place and form in their organism. The second great class of alimentary bodies consists of starch, sugar, gum, and fat, which contain no nitrogen, and therefore cannot build up animal organs having fifteen per cent. of that element. Their main function, according to Liebig, is to support animal heat, which, in the warmblooded animals, is always considerably above that of the surrounding atmosphere. These substances burn readily, and produce a large amount of heat in their combustion. The gaseous products of their union with oxygen are carbonic acid and water, precise. ly the same bodies which escape from the human lungs. Combustion within the body is attended with the evolution of as much heat as when it takes place actively outside the body. The fact that there is flame în accident of the rapidity of combustion. one case, and not in the other, is the mere When iron rusts in air, it gives out just as much heat as when it burns with bright scintillations in a smith's forge, but the evolution of the heat is spread over a longer time. So when sugar or starch burns within the body, the amount of heat developed is the same as if they were consumed in an open fire; the only difference is, that the heat, being produced slowly in the former case, is absorbed by the blood and tissues of the animal, so as to heat them to a temperature of about 99 degrees Fahrenheit. This alimentary fuel enables the body of man to retain a uniform temperature under the most varying conditions of climate, for the appetite regulates the amount required to sustain the animal heat. Modern physiology is not so restrictive as Liebig was in his first announcement of this division of alimentary substances into flesh-formers and heat-producers; for while it is admitted that albuminous bodies have for their special function the formation of the organism, it is now certain that they can also act in the maintenance of animal heat. The second class, or the non-nitrogenous bodies, cannot perform this double office. They may, and no doubt do, act chiefly as the heat-givers,' but they never can play the part of flesh-formers.'

This brings us back to our main subject; for while chemists agreed upon the view that starch, sugar, and fat cannot form the organs of the body, they are in conflict as to their power of producing muscular force. One section of chemists, headed by Liebig,

contend that the main function of nonnitrogenous food is the production of animal heat and not of muscular force, while the other section believe that muscular power is their primary function, and animal heat the secondary effect. Both sections of chemists rely upon numerical results in support of their views, and we proceed to describe the manner in which these are obtained. When a man is at rest, he expires a certain quantity of carbonic acid; when at work, a much larger quantity. Thus a laboring man, during one hour of rest, exhales 130 grains of carbon in the form of carbonic acid, and during one hour's work, 530 grains of carbon. This excess of carbon burned in the body during work is viewed by many chemists as a proof that starch, sugar, and fat-the non-nitrogenous fuel-is consumed in the muscular force which enables the laborer to do the work. At all events, three-fourths of the increase must be due to such bodies. But while gaseous carbonic acid escapes from the lungs, a solid form of carbonic acid, containing nitrogen, or amidocarbonic acid, passes away in solution per vesicam, having been secreted by the kidneys. It is well known as urea, and is the representative of wasted muscles when no food has been taken, and of these, plus any excess of albuminous food beyond that required for the supply of waste, when too much aliment is introduced to the body. Besides this urea, which is the chief constituent of the ural secretions in man, small quantities of other nitrogenous ingredients are found, but for our present purpose are unimportant. Suppose that a laborer lives without gluttony, it is only necessary to ascertain how much urea has passed out per vesicam in twenty-four hours, then to multiply this amount by three, and we obtain the quantity of dry flesh which has been wasted during the same time by the wear and tear of the body. It is agreed that ordinary men, in good health, evacuate 520 grains of urea in twenty-four hours, while they emit the equivalent of 65 grains by other secretions; hence we ought to find, multiplying these numbers by three, that they should have 1755 grains of albuminous substances in their daily food. The experience of mankind does in fact show that they consume four ounces, or 1750 grains daily, of dry albumen, so that theory and experience in this respect closely agree. A really hard-worked labourer passes between 700 and 800 grains of urea daily, and consumes 5 ounces of dry albuminous food. As it is possible, then, by means of the excretions, to ascertain the extent of muscular waste, it becomes a mere matter of calculation

to determine whether the amount of potential energy resident in the wasted muscles suffices to account for the work performed, or whether it is necessary to supplement this by the combustion of the non-nitrogenous portions of food. The potential energy in flesh resides in the chemical affinity which it possesses for the oxygen dissolved in arterian blood. The oxidation resulting in the display of energy has been calculated by Playfair to produce as much heat as is represented by 4450 calorific units. In other words, one gramme of flesh in oxidizing could heat 4450 grammes of water one degree of the centigrade thermometer.* A year after this estimate, made upon theoretical considerations, Frankland experimentally determined the calorific value of beef muscle, and found it to be 4368 units; and as the experiments differ about 100 units from each other, we may safely assume Playfair's theoretical estimate and Frankland's experimental one to be identical, and take 4400 as in round numbers the calorific value for one gramme of flesh. The beautiful researches of Joule have taught us how to express a certain amount of heat by its representative of mechanical work. His experiments show that if we multiply the above number by 425, the mechanical equivalent of heat is obtained; or the product signifies the number of grammes weight which could be raised to the height of one metre by the potential energy of the gramme of muscle. The figures thus obtained being too large to deal with conveniently, it is usual to refer to kilogrammes (1000 grammes), and to indicate the mechanical work of so many kilogrammes raised to the height of a metre. Calculated in this way, one gramme of dry flesh or albumen (15,43 grains English) has potential energy enough to raise 1870 kilogrammes to the height of one metre. As the ordinary diet of a man is four ounces or above 113 grammes, he ought to have in the transformed muscles of his body potential energy enough to raise 211,310 kilogrammes to the height of a metre. The actual external work of such a man is rep presented by a daily march of seven miles, which is the common soldier's exercise when in barracks, and this represents only 38,000 metre kilogrammes of work. Deducting from the potential energy 60,000 metre kilogrammes for the internal work of the body, such as the action of the heart, lungs, and

* We use French weights and measures, in deference to the growing feeling that the metric system should be followed by this country in all subjects relating to science. A kilogramme equals 2.2 lbs. English, and a metre 1.09 yard, or a little more than 39 inches.

intestines, all of which exercise mechanical | enhaim, however, has shown that a muscle force measurable in amount, we have still, during work may convert as much as oneaccording to Playfair, upwards of 150,000 half of its energy into useful work, and if metre kilogrammes of energy to do 38,000 we take this as the utmost limit of economy of actual work. A prima facie case is thus of the human machine, we must admit, with made out for Liebig's view that muscular Fick and Wislicenus, that not one-fourth of waste may be the source of work in animals. their labor in ascending the Faulhorn could His opponents, however, proceed to test be attributed to the muscles expended in the it by inducing excessive work, and ascertain- effort. Their conclusion, therefore, appears ing whether that is attended by a cor- justified that the non-nitrogenous constituresponding excessive waste in the muscular ents of food, the starch and sugar upon system as displayed by a large increase of which they subsisted, must have helped them urea in the secretions. With this view, two to accomplish the work, or, as they contend, philosophers of Zurich, Fick and Wislicenus, have been the whole source of the power. ascended the Faulhorn, a mountain which These experiments have been taken by every one knows rises above the lake of Frankland and others without cavil, and are Brienz to a height of 2000 metres. For assumed to be quite conclusive. To our thirty-one hours previous to the ascent, they mind they are not so, and contain within fed themselves on starch and fat, the chief them grave errors. The chief objection to non-nitrogenous constituents of food, obvi- their conclusiveness is, that the period of ously for the purpose of relying on the al- production of urea within the body is not ready formed muscles in the body to accom- the period of its elimination from it. Dr. E. plish the ascent, if the power resided in Smith, in his experiments on prisoners on them. During the night previous to the as- the treadwheel, and on himself, in the daily cent, they determined the amount of urea avocations of his profession, has shown that secreted, then that eliminated during climb. irregularities in labour and diet, and even ing, ascertaining also the quantity passed in changes in the barometer and thermometer, the six hours succeeding the work, and retarded the secretion of urea, so that the finally the amount secreted during the night quantity produced in one day may not pass after they had partaken of a hearty dinner, away till the second or even third day. Prefrom which meat was no longer excluded. cisely these conditions were present on the The experiment was in fact of remarkable Faulhorn, for at the summit there was a low interest, and seemed to give all the necescondition both of atmospheric pressure and sary data for the determination of the ques- temperature, the very conditions which had tion. The weight of their bodies and accou- previously been pointed out as powerfully trements having been determined before retarding the elimination of urea. The phistarting, and the height of the mountain be- losophic mountaineers ascended under a peing known, the number of metre kilo- culiarly unusual diet; their starch cakes, grammes of work performed by them in the fried in fat, must have tested their digestive ascent could be estimated. Was this work powers in no common degree. Under normal represented in the urea formed during the conditions of diet, the amount of nitrogen ascent and for six hours after it? The in the solid excretions is only about oneamount of urea secreted during the ascent twelfth that in the liquid; but if there are and for six hours after it showed that thir- digestive difficulties to overcome, as when a ty-seven grammes of dry muscle had been dog is fed on starch and fat alone instead of wasted, and these could have developed sev- flesh, then the amount of nitrogen in the enty thousand metre kilogrammes of me- solid excretions increases, according to Bischanical force. But in raising the body to chof and Voit, to an amazing extent, generthe top of the mountain, and in supporting ally exceeding the amount in the liquid the action of the heart and respiratory excretions. The reason for this augmentaorgans during the ascent, the pedestrians had tion is, that the solid excrements of an aniactually expended nearly one hundred mal chiefly consist of the exhausted ferments and sixty thousand metre kilogrammes of used up by the digestive fluids in overcomforce, or more than double the amount which ing difficulties to assimilation. Now Fick could have been afforded by the transforma- and Wislicenus have overlooked this circumtion of the muscles. This assumes that all stance altogether, and do not tell how much the potential energy resident in the muscles nitrogen was present in the alvine secrecould be converted into useful work. Now, tions. In the absence of such information, with all the improvements in the steam- their experiments lose much of their value. engine, only one-tenth of the power Even on their own theory, that the animal evolved from the fuel while burning is body is a machine like a steam-engine, suptransformed into mechanical work. Haid- plied with non-nitrogenous fuel, and exhibit

ing a waste displayed in the urea as a consequence of mere tear and wear, we should have expected that the urea, as the representative of the friction of the machine, should have been increased proportionately to the heavy work of the ascent, although the actual increase might have no numerical relation to the origin of muscular force. The following numbers are those given :

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22

38"

16

32

The experiments, in fact, prove a great deal too much, for while they indicate that the urea is not secreted in proportion to the work performed, they show likewise that when the machine is exposed to heavy tear and wear by excessive work, the waste by friction is considerably less than it was for the twelve hours before the ascent, when the pedestrians slept comfortably in their beds on the shore of the lake of Brienz. This fact ought to have made them suspicious either that all the waste matter had not been eliminated during the short term of their experiment, or that it had escaped in other directions than per vesicam.

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a compensating action as regards muscular energy. Nitrogenous fuel might be the ordinary and proper material for muscular action; yet, as a temporary substitute, nonnitrogenous fuel might be applied, not, however, without a certain deterioration of the machine. It is therefore possible that, if all the necessary corrections were made to the experiments of the Zurich physiologists, there would still be found a large amount of actual work which was performed by the use of starch and fat as fuel, in substitution of 46 grammes. that which is commonly employed. In the case of underfed and overworked prisoners,' carrying out their punishment on the treadmill, Dr. E. Smith found that more work was performed than could be attributed to wasted muscle, but the men were running down in strength, and could only be put upon their labor every second or third day. This modified view of the subject is not admitted by Frankland and his supporters. They contend that not in man alone, but in lower animals, there is evidence that the non-nitrogenous food-the starch, sugar, and fat-is the source of muscular work. Bees are brought in support of this view, for honey consists chiefly of sugar, and contains but a small amount of nitrogen as an albuminous mixture. Yet bees subsist upon honey only during the winter, precisely at that period of the year when they have scarcely any work to perform. During summer, when they work hard to form this winter store, their food is not exclusively saccharine, for the pollen of flowers, which, in the form of bee bread, forms the chief food of the larvæ, is also consumed by the working bees, and is in itself highly nitrogenous. The mouth of the butterfly is only adapted for the suction of honey from flowers, and yet it uses much muscular exertion in its lengthy flights; but we are certainly sceptical as to Verloren's statement that this honey is free from nitrogen, for the excrements of butterflies are rich in that element, and can only have been derived from the food taken. Insects are cited by the advocates of the view now under consideration as offering powerful arguments in favour of their theory, but they may likewise be brought in strong opposition to it. For the theory supposes that the non-nitrogenous fuel is brought in the blood to the muscles, where it is used for the production of mechanical effects; but as insects have no true blood, it is difficult to see how they support this view.

For the reasons stated by us, we do not consider that the celebrated ascent of the Faulhorn has settled the important question of the origin of muscular force in man. Nevertheless, we are not inclined to disbelieve the view that occasionally, and under peculiar circumstances, the corporeal machine may be fed with non-nitrogenous fuel. Vicarious action is common in all parts of the body. The skin assumes the functions of the kidneys when their action is retarded; the latter, and even the intestines, remove those portions of water from the system that impaired lungs are unable to carry off as vapour. Both the skin and the lower intestine can, under exigency, perform the function of the upper intestine in absorbing food, as instanced in the nutritive injections and soup-baths which supported a former King of Prussia in his last illness. The stomach occasionally does some of the duties of a defective uterus. When the blood refuses to oxidize non-nitrogenous fuel so as to convert it into carbonic acid exhaled by the lungs, the skin comes to its aid, and removes it in the form of marsh gas. In fact, all through the body, means are provided for effecting, under difficulties, by extraordinary means, the ordinary actions intrusted to certain So that it is not surprising to find

roans.

We have endeavoured to state fairly the views of one set of chemical physiologists, though we have not hesitated to express our dissent from them in some cases; and

we now proceed to discuss the opinions of their opponents.

There seems to be no doubt that the oxidation of the substance of a muscle can produce muscular force. If a living bundle of muscular fibre, white and free from blood, be excited electrically, it shows muscular irritability by contracting, and, if attached to weights, will raise them, thus doing actual work. The amount of electricity required to produce this irritability is so small, that it has no relation whatever to the work performed. A muscle is only contractile in the presence of oxygen gas, so that its work is obviously the result of oxidation. But as muscular fibre contains fat, a non-nitrogenous substance, as well as nitrogenous fibrin, its contractility might be supposed to be due to the former body and not to the latter. Helmholtz has discussed this question by examining the changes of a muscle before and after contraction, and he found that, while the substance of the muscle wasted by oxidation, the fat remained unaffected. Electric excitement is not always necessary for its manifestation. We have seen the heart of a shark removed from the animal and drained of blood exhibit its regular valvular action for a quarter of an hour. The head of the same fish, cut off from the body, can bite fiercely with its jaws for some minutes. This retention of muscular power is well marked in a curious fish of the White Nile, the Tetrodon Physa, regarding which Baker states that many minutes after the head had been severed from the body the jaws nipped with fury anything that was inserted in the mouth, nipping through thin twigs and thick straws like a pair of shears.' The heart of the turtle continues its action for a long period after being extracted from the newly-killed animal. The irritability of a muscle removed from the body, cut off from blood, and working under electric excitement or spontaneously, seems without question to derive its power from the oxidation of its own material. And if this be true of detached muscular fibre without the body, it is probably also true of muscle in situ within the body. There is, in fact, no doubt that nitrogenous substances free from fat can support muscular force perfectly well, the only question being whether they act as fuel external to the muscle, or are first built in as part of its structure before being used to produce muscular power. The Jews, who have retained the characteristics of their race, as well as their corporeal health and mental activity, for a long series of years, carefully remove fat from their food before eating it, in obedience to the Levitical law: This shall be a perpetual

statute for your generations, throughout all your dwellings, that ye eat neither fat nor blood.' As the chemist may, however, contend that a mere mechanical separation does not take away all the fat concealed within the muscular fibres, we proceed to quote experiments to which this objection does not apply. Two German physiologists, Bischof and Voit, carefully freed flesh from all its fat, by chemical means, and fed a dog upon it for a month; this dog kept perfect health, and worked a treadmill doing 150,000 metre kilogrammes daily. Savory fed rats on a similar diet, and found that they also could live well on nitrogenous matter free from fat, starch, and sugar, and carry on' their usual muscular efforts. The purely nitrogenous diet had thus a double power for while it kept the muscles and other organs of the body in repair and fit for their usual functions, it at the same time supported the animal heat. Non-nitrogenous diet cannot effect this double purpose, for, though well-fitted to support the internal heat, it cannot repair wasted tissues, and therefore is not fitted to support life per se. Bischof fed a dog upon a mixed diet of flesh and fat, increasing the proportion of the latter gradually, and found that, while the fat was laid on to the body, the nitrogenous portion of the food became oxidized in preference, and appeared as urea in the excretions, showing that it is peculiarly susceptible to that oxidation which is the origin of all force in the body, whether it manifests itself as heat, electricity, or muscular power.

If our readers have followed these observations, they will find the question much narrowed. There is now a common agreement among all chemists and physiolo gists:—

1. That purely nitrogenous diet can support living tissues and produce muscular force.

2. That non-nitrogenous diet per se cannot support living tissues, or permanently sustain muscular force.

The question is now limited to this: In the mixed diet of mankind is there sufficient nitrogenous matter to account for muscular force under ordinary circumstances? Frankland denies this in the lecture which we have quoted, and Playfair affirms it. The latter chemist appeals to the ordinary ex. perience of mankind, and refuses to allow abnormal experiments, such as those of Fick and Wislicenus, to be considered as bearing on the question; for while he does not deny that muscular force may be exceptionally produced by the combustion of non-nitrogenous fuel, he at the same time contends that this source cannot be continuously re

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