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THE ORIGIN OF MUSCULAR POWER.

and tissues of the body. If the views advocated by Traube, Haidenheim, and Frankland be correct, the development of animal heat is, however, to be regarded as a residual and secondary, though by no means an unimportant physiological result, the development of muscular energy being first provided for, whilst the animal heat developed is the necessary residuum of the transformation of energy into muscular power, even when the muscular power is exerted externally.

(1726) On the Origin of Muscular Power.-It is now admitted by both physiologists and chemists, that muscular power is derived from the action of the oxygen supplied during respiration upon the digested portions of the food, either in their circulating condition as constituents of the blood, or after they have become part of the tissues of the living body. But it is still a matter of dispute whether these constituents must be first converted into actual muscle before their oxidation can give rise to mechanical force; or whether it be not possible that muscular work may also be derived from the oxidation of the constituents of the blood, in their passage through the muscle, and though they may be unfit for conversion into muscular fibre.

Liebig distinctly maintains that the non-azotised portions of the food are mere heat-givers, and that the transformation of the azotised tissues is the source of the dynamical power of the animal.

This view has been largely accepted; it is still supported by Ranke, by Playfair (see his lecture "On the Food of Man in Relation to his Useful Work," published in 1865), and by many men of eminence. On the other hand, it has been opposed by J. R. Mayer, who distinctly stated in 1845, that "a muscle is only an apparatus by means of which the transformation of force is effected, but it is not the material by the change of which the mechanical work is produced;" and he regards "the blood, a slowly-burning liquid, as the oil in the flame of life." Lawes and Gilbert were led to similar conclusions from their observations on the feeding of cattle, and Mayer's view has recently received experimental confirmation from Voit and from Ed. Smith, and particularly from Fick and Wislicenus, Phil. Mag., 1866, and from Frankland (Ibid.).

For the satisfactory solution of this important problem, the following data are requisite:

Ist. The amount of force which can be generated by the oxidation of a given weight of muscle in the body.

2nd. The amount of force actually exerted by the muscles in the body during a given time, and

THE ORIGIN OF MUSCULAR POWER.

943

3rd. The quantity of muscle actually oxidized in the body during the same time.

If the total amount of work performed in the given time be greater than could possibly be generated by the oxidation of the muscle consumed during the same time, it necessarily follows that the power of the muscles is not derived exclusively from their own substance.

1st Datum. To determine the amount of force generated, it is necessary to agree upon a unit; and the unit which is now generally adopted for the measurement of mechanical force is that which is represented by the lifting of a kilogramme to the height of a metre, or, as it is commonly termed, a metre-kilogramme (mkg.). The connexion between this unit and the amount of heat which it represents is supplied by the experiments of Joule, who has shown that an expenditure of heat sufficient to raise 1 kilog. of water 1° Centigrade would suffice to raise 1 kilog. to the height of 423 metres, or 423 kilogs. to the height of 1 metre; and conversely, that the fall of 1 kilog. from the height of 423 metres, or of 423 kilogs. from the height of 1 metre, would develop an amount of heat, when the weight is suddenly brought to rest, sufficient to raise 1 kilog. of water 1° C. Consequently 423 metre-kilogs. of force are required to raise I kilog. of water 1° C.

The first datum has been given by Frankland; for he finds that if I gramme of dry muscle be burned in oxygen, it will give out a quantity of heat which will raise 2161 kilogs. to a height of 1 metre. Consequently it is impossible that the consumption of a gramme of muscle in the ordinary wear and tear of the body can produce a force greater than this. If, in climbing, for example, 2161 kilogs. be lifted to a height greater than I metre by the waste of 1 gramme of muscle, it is certain that the oxidation of something besides muscular tissue must have taken place. In reality, however, the muscle never leaves the body in a completely oxidized form; it passes off mainly in the shape of urea, which when burned still gives off heat equivalent for each gramme to 934 mkgs. Now as muscle and albumen would furnish almost exactly one-third of their weight of urea, the quantity of heat emitted by 1 grm. of muscle during its conversion into urea would amount to 1848 mkgs. instead of the full 2161 mkgs. (Frankland).

2nd Datum, the amount of muscular force actually exerted in lifting a known weight in a given time to a known height. Fick and Wislicenus have attempted to furnish this by climbing a steep mountain, the weight lifted being their own bodies, the altitude

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THE ORIGIN OF MUSCULAR POWER.

of the mountain being known. At the same time they endeavoured to obtain the

3rd Datum―viz., the quantity of muscular tissue expended in producing this amount of exertion, by determining the quantity of nitrogen excreted by the kidneys during the effort, and comparing it with that which escaped by the same channel before and after the exertion. They assume that the whole of the nitrogen of the metamorphosed tissues passes off in the urine, and of course the accuracy of their result depends on the truth of this assumption, which is pretty generally adopted by physiologists.

It would occupy too much space to go in detail into the precautions adopted, or into the objections which may fairly be raised against the manner in which this ingenious method of attempting to solve the problem was carried into effect.

Instead of allowing themselves their ordinary diet during and after their experiment, the Swiss professors placed themselves for the day before upon a diet free from nitrogen, and ate a plentiful meal after their exertion was concluded. The precaution thus adopted produced a paradoxical result; for during the effort of climbing, which lasted 5 hours, less nitrogen was excreted in the urine than escaped through this channel during the same period of repose before the exertion commenced.

Imperfect, however, as the results are at present, they yet possess a high degree of interest, as will be seen from the considerations which follow.

The height of the Faulhorn from the lake of Brienz at the point selected was 1956 metres; the weight of one of those who made the experiment was 66 kilogs., and the time occupied was 5 hours. But the effort required to raise the body to a given height is by no means a complete measure of the muscular exertion made in the time. The heart is in perpetual action, the ribs are in alternate rise and fall, the peristaltic and other movements are constantly going forward; and last, not least, the state of tension into which the various muscles are thrown during the whole time, in order to preserve the body in the erect position, is continually exhausting muscular energy within the body. In this ascent the average number of pulsations per minute was in Fick's case 120; and it has been calculated that each beat of the heart of a man of ordinary stature and strength is equivalent to o 64 metre kilogrammes, whilst, according to data furnished by Donders, an ordinary inspiration of 36.6 cub. inches (600 cub. centim.) represents 063 mkg., and Fick's inspirations averaged 25 per minute during the ascent.

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945

No satisfactory measures of the amount of exertion expended in maintaining the muscular tension have been made, but from the incomplete data we possess it cannot be less than equal in amount to the effect manifested by the weight raised in climbing. The amount of force expended by one of these gentlemen (Professor Fick) in climbing was therefore:

Min. Hrs.

Mkg.

Metre kilogrammes.

Metre. Kilo.

1956 × 66

weight raised = 129096 120 × 60 × 5'5 × 0.64 pulsations = 25344 25 × 60 × 5'5 × 0.63 respirations = 5197 Muscular tension not calculated.

159637

=

This would require a consumption, according to Frankland's estimate, of 1937-86.3 grammes, if the whole of the nitrogen of the muscle were converted into urea. Now, the nitrogen found in the urine during the ascent amounted to

So that the total quantity of muscular fibre which was oxidized in the ascent, if measured by the urine, and if the whole of the urea excreted during the following 6 hours be included, scarcely amounts to more than one-third of the quantity necessary to occasion the effect, without taking into account the quantity expended in producing the muscular tension, which probably would require at least an equal consumption of material to maintain it. So far, therefore, as these experiments go, it appears to be clear that something besides azotised material was expended in maintaining the energy manifested in the ascent. It must be added that the results furnished in the case of Wislicenus likewise confirm these conclusions most completely.

No doubt it will be urged, and with justice, that in order to enable us to draw rigorous conclusions, experiments of this kind should be prolonged for several days in succession, that the food taken should be such as the observer is habitually accustomed to take, and that careful analyses of the urine should be made for several days before and several days after those devoted to the ascent. There is also no doubt that experiments on the tread

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PROCESS OF SECRETION.

wheel, as practised by Dr. Ed. Smith, admit of far greater precision than these of the Swiss professors, though it requires rare steadiness of purpose to carry them through.

(1727) 3. Secretion.-Having now considered the functions of the blood in regard to nutrition, and to respiration, we have lastly to offer a few remarks upon the process of secretion. It is worthy of remark that in every instance where a purely excrementitial matter is formed, the substances excreted are produced in the mass of the blood, at a distance from the point at which they are separated. The bile furnishes an exception, but, as it has been already stated, the great proportion of this fluid is re-absorbed into the system; it therefore cannot be considered as purely excrementitious. In experiments in which the kidneys have been removed from animals, uric, phosphoric, and sulphuric acids, as well as urea, are found to accumulate in the blood; the kidney is, therefore, not to be looked upon as an oxidizing or acidifying organ, but as an organ through the agency of which acids are separated from the system, combined with, and nearly neutralized by, alkaline matters. A similar principle holds good in the case of the lungs, which may be viewed as a gland by which carbonic anhydride is excreted; the carbonic anhydride, however, not being formed by the lungs, but simply eliminated by their action. It appears, therefore, that those organs which are destined for the separation of excretions from the body do not form the various substances, but simply eliminate them. But the case is otherwise with the glands which furnish substances destined to be consumed subsequently by the economy: these glands in such instances seem to effect a true transformation of the blood, one part of which forms the peculiar matter of the secretion (as for example, sugar of milk in the mammary gland), the other, or complementary portion, is returned into the mass of circulating fluid. The true mechanism of secretion is at present unknown. It has been imagined that secretion may present a certain analogy with the case of vinous fermentation, in which, little as we know of the cause, we understand the conditions requisite to produce it; for it appears that the main point consists in the presence of certain organic molecules, since it is found by the experiment of placing yeast in a tube closed with filtering paper, and dipping it into a solution of syrup (p. 154), that actual contact with those molecules is necessary to produce the decomposition, the liquid in the tube being the only part which ferments: hence we may conceive why blood out of the gland undergoes not the same changes as when circulating