520 



NATURE 



[March 28, 1895 



If we pre»ent a muscle from doing external work during the 

 contraction, the whole actual energy will present itself in the 

 shape of heat. When there is but a slight contraction, the 

 muscle of a frog, e.g., will grow warmer by about oooi" C. 

 Supposing the specific heat of the muscle to be equal to that 

 of water (in fact it is less), we find that for a rise ol 0001° C. in 

 temperature a ijuantiiy of heat of oooi cal. is required for 

 each gram of muscle. No matter whether this quantity of 

 heat results from the combustion of carbohydrates, fats, or albu- 

 minous matter, it can be but an infinitesimal part of the mus- 

 cular substance that produced it. If, t.g., as is ordinarily sup- 

 posed, the combustion of a carbohydrate into COo and H«0 

 produced that heat, taking the heat of combustion ol one gram 

 of carbohydrate to be broadly 4000 cal., no more than a four- 

 thousandth part of a milligram will have been consumed in each 

 gram of the muscle. Hence only about a four-millionth part of 

 the muscular substance could have been the source of the actual 

 energy set free by the stimulus, and at the same time, accord- 

 ing to the above hypothesis, have been the subject of direct 

 attraction. 



But whatever may be our conception of the size, form, 

 position, and sphere of action of this four-millionth part in 

 relation to the other soft, watery mass, only passively moved, I 

 fail to understand how, through direct chemical allniilion, this 

 one minute part should bring about the movement of the rest of 

 the four million parts in such a manner as it does. 



The adherents of the chemico-dynaniic hypothesis have not 

 answered this objection as yet. And since they can give but 

 an unsatisfactory account or no account at all of many other 

 fads (I will refer to some of these facts further on), we may be 

 allowed tu cast about for some other explanation. 



The EUetrodynamic Hypothesis. — Since Galvani's discoveries, 

 the electric phenomena of muscles have frequently been sus- 

 pected to contain the solution of our problem. And, indeed, 

 it is not so very difficult to mention a series of facts which seem 

 to bear out the suggestion that the mechanical work done by 

 the muscle may be created from chemical energy through the 

 medium of electric forces. 



There is, in the first place, the fact that muscles, when in 

 action, produce regular electiic effects. These effects are in- 

 deed the first phenomena we can observe after stimulation. 

 They seem to begin at the very moment of stimulation, shortly 

 before the contraction, hence they might in so far be the cause 

 of the mechanical process. 



Moreover, as du Bois-Reymond proved, the value of the 

 electromotor force is very high, and in the active particles is 

 probably much higher than the force of the currents we can 

 derive from the surface of the muscle. 



.\dd to this that the economic corfficienl of the muscle may 

 attain, just as in the case of electric motors, a considerable pro- 

 poition. .As much as 25 per cent, and more of the potential 

 enetcy which has been consumed may be transformed into 

 mechanical \\ ork. 



Howtver, there are weighty objections to this hypothesis 

 also. In the first place, there is the fact that these very same 

 electromotor forces, of cjual intensity and direction, appear, 

 under the same influences, not only in the muscles, but al-o in 

 nerves, glands, and other organs, which do not pos.sess the least 

 contractility. Then there is the important discovery of 

 Biedermann, that the contractility of muscles maybe completely 

 neutralised by water or etheric vapours, without doing any 

 perceptible harm to the electromotor phenomena. 



In the same way the development of (he electric organs sup- 

 plies us with important proofs of the independence of the 

 eteciiic and the mechanical processes. In most cases these 

 organs are developed out of striped muscular fibres. Now, in 

 this process of development, contractility is gradually lost, 

 whereas the power of producing electrical effects attains a yet 

 higher degree ol perfection. 



The Thermodynamic Hypotlusi.. — More probable than the 

 chemical and the electrical hypothesis may be deemed a sug- 

 gestion, first put forward by Jul. Rob. Mayer, though in an un- 

 tenable form, according to which the muscle is a thermodynamic 

 machine. I'hysiologiss, however, generally object that this 

 view is not compatible with the second law of thermodynamics, 

 for we cannot expect differences in temperature in the muscle 

 •o great as this law requires they should l>e. 



Now I venture to thmk that, on the contrary, we mu^>l ssume 

 exceedingly great differences of temperature in the stimulated 

 muscle. What holds good of the whole body holds good of the 



NO. 1326. VOL. 51] 



muscle also ; the tenipei.iture, treasured with our instruments, 

 is but an arithmetical aveiage, " comprising an infinite number 

 of different temperatures, pertaining to an infinite number of 

 different points" (rfliiger). 



From the fact that at the contraction an infinitesimal part 

 only of the muscular mass is chemically active, we infer that 

 the temperature of these particles must, at the moment of com- 

 bustion, be an uncommonly high one. Great as the specific 

 heat of muscular substance is, it would otherwise be impossibls 

 to account lor a rise in the temperature of the whole mass even 

 of o"ooi° C. only. 



Since each thermogenic particle is surrounded by a relatively 

 enormous cool mass, conducting heat and diathermanous, the 

 principal condition for the transformation of heat into 

 mechanical work has been satisfied, and, on .iccount of the 

 enormous diflerences in temperature which we h-tve to assume, 

 satisfied to such a high degree, that even an economic co- 

 efficient of 30 percent., nay, 50 per cent., and even more, seems 

 to be theoretically possible. 



Supposing we have to deal with a Carnol's cvcle, the theo- 



T - T„ 

 retical maximum Q„ of the mechanical effect is Q,, = Q ^^ - — > 



'1 

 where Q stands for the whole quantity of heat, which from the 

 absolute temperature T, is sinking down as far as T„. Taking 

 T„ = 273 -r 37 = 310 , the mechanical cfl'cct might at Tj = 

 410" amount to 30 per cent., when the temper.iture of the 

 active particles would consequently exceed the average 

 temperature of the normal muscle by 100° C. only. 



The objection that these high temperatures must necessarily 

 destroy the life of the muscle, since the latter becomes rigid 

 and dies even at 50 C, is, for the same reasons, of small im- 

 portance only. For it is ever but an infinitesimal part of the 

 muscular mass that is exposed to these high temperatures. At 

 a small distance from these furnaces ol heat the temperature 

 must have fallen so low as to be haimless. The muscle will 

 no more be destroyed by stimulation than a steamer will be 

 de.'^troyed by heating the furnaces. 



However likely it may thus seem that nature should avail 

 herself of these favourable terms on which mechanical work 

 may result from muscular heat, we have up to the present time 

 no direct proof that this is actually the case, nor do we know 

 in what way it takes place, if in any. But I venture to think 

 that the proof can now be given, inasmuch Jis it is possible to 

 demonstrate how, through the medium of peculiar arrangements 

 of the material of the muscle, a transformation of chemical 

 energy into mechanical work by means cf heat not only can, 

 but actually must, be brought about.' 



Muicular Structure in relation to Contractility. 



7 he Fibrils are the Scat cf the Shortening Power.— Vox this 

 we need firstly to pay attention to the peculiarities of the micro- 

 scopical structure of muscle. All muscular fibres of all animals 

 are composed chiefly cf two parts : extremely thin, lonf;, 

 albuminous fibrils, and an interfibrillar plasmatic substance, 

 the so-called .'■arcoplasma. The quantitative relations of both 

 vary, but the fibrils always occur rn great number, forming very 

 often the greatest part of the whole mass of the muscle. They 

 always run parallel to each other throughout the length of the 

 fibres. 



This fibrillar structure is also presented by all the other formed 

 contractile substances. 



Direct microscopical observation during life teaches us that 

 the fibrils, and not the saicoplasm, are the seat of the shorten- 

 ing power. The fibrils in a state of relaxation are long and 

 thin, and often run in winding curves, but grow short, thick, 

 and straight, in consequence of stimulation. The sarcoplasm 

 passively follows their movements. Moreover, completely 

 isolated fibrils can shorten. 



Jhe Tilirils arc Contractile lecause they contain Doubly 

 A'c/ractiTe /'articles.— Thvs the question arises : Can there l)e 

 demonstrated in the fibrils such arrangements of their material 

 as by their mediation contractile loicc may originate in a 

 thermodynamic way ? 



Light— /«.!■ optimum -eagens, as Buys Ballot said— solves this 



' The tuipirical found.ilions of ihe views Jcvc'opcd in ihis lecture will 

 be fuiind in "VcMUchc iilxr Aftiderunscn dcr Fotm und derelaslischen 

 Ki.ifle doiipeIbrcct)cndcr Gewtliiclenicnlc untcr ct.cnii*chcn und lliernii- 

 »chen tindu^fccn," in the Arpcridix of my Memoir. " Ucbcr den Ursprunft 

 der M\iflielkrnfl "(ale Auflagc. Lcip/ig. lE<)3. S. 5<eo), and in tlic 

 iiler.iliirc ritcd in ihc same paper. 



