THE CHEMISTRY OF MUSCLE. 73 



from plain muscle. The apparatus is illustrated and described in Fig. 27, 

 and the curve of contraction obtained from it is shown in Fig. 28. The under- 

 lying principle of this hypothesis has met with much criticism. Fick * has 

 shown apparently that when applied quantitatively to the work done by muscle 

 it leads to an impossible conclusion. If, in a reversible process, at a temper- 

 ature T , a certain quantity of heat, Q , is converted to mechanical work, it 

 necessitates, according to the second law of Thermodynamics, the passage of 

 heat, Q, from a higher temperature, 1\ to a lower temperature, T 2 , in accordance 



with the equation, ~ = Q ( , - -=7- I 

 *a \ -M -M / 



Fig. 28. Curve of simple contraction obtained from an artificial muscle. The dura- 

 tion of the stimulus (heating effect caused by the current) is shown by the break in the 

 line beneath the curve. 



We may assume, in accordance with experimental results, that the efficiency 

 of muscle is equal to 25 per cent, of the total energy, or that Q = jQ, and that 

 T 2 is the temperature of the body, 37 C., or expressed in the absolute scale, 

 37 + 273 = 310 C. T is the same as T,. If, now, in the equation we sub- 

 stitute |Q for Qo and 310 C. for T 2 and solve the equation for T\ it gives a 

 value of 387 C., or, expressed in centigrade units, 387 273 = 114 C. 

 That is to say, to perform the work indicated the muscle must show a fall 

 in temperature from 114 to 37 C., and it seems clearly impossible to sup- 

 pose that the muscle in contracting attains any such temperature as 114 C. 



This criticism has been accepted by most authors as demonstrating that the 

 muscle cannot work as a heat engine by transforming a part of the heat of the 

 chemical reaction to work. A difference in temperature is necessary that is 

 not possible in the case of muscle. Other theories have been proposed, accord- 

 ing to which the chemical energy is supposed to be converted into work either 

 directly (Fick) or through a change in surface tension. The muscle is supposed 

 to act in such theories as a chemical or chemodynamic engine. The various 

 forms which the theories employing the conception of surface tension have 

 taken make it difficult to describe them in general terms. According to one 

 presentation (Macallumf) the sarcous elements (dim bands) may be considered 



* Fick-Pfliiger's "Archiv," 1893, 53, 606. 



t Macallum, "Surface Tension and Vital Phenomena," University of 

 Toronto Studies, Physiological Series, No. 8, 1912. 



