416 Prof. Th. W. Engelmann. [Mar. 14, 



The Thermodynamic Hypothesis. More probable than the chemical 

 and the electrical hypothesis may be deemed a suggestion, first 

 put forward by Jul. Rob. Mayer, though in an untenable form, 

 according to which the muscle is a thermodynamic machine. Physio- 

 logists, however, generally object that this view is not compatible 

 with the second law of the theory of heat, for we cannot expect 

 differences in temperature in the muscle so great as this law requires 

 they should be. 



Now I think that, on the contrary, we must assume exceedingly 

 large differences of temperature in the stimulated muscle. What 

 holds good of the whole body holds good of the muscle also ; the 

 temperature, measured with our instruments, is but an arithmetical 

 average, " comprising an infinite number of different temperatures, 

 pertaining to an infinite number of different points " (Pfliiger). 



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 combustion, be an 

 uncommonly high one. Great as the specific heat of muscular 

 substance is, it would otherwise be impossible to account for a rise 

 in the temperature of the whole mass even of O'OOl C. only. Without 

 any exaggeration we may assume that the temperature of the 

 chemically active particles may, at the moment of combination, exceed 

 the average muscular temperature by hundreds of degrees. 



Since each thermogenic particle is surrounded by a relatively 

 enormous cool mass, conducting heat and diathermanous, the prin- 

 cipal-condition for the transformation of heat into mechanical work 

 has been satisfied, and, on account of the enormous differences in 

 temperature which we have to assume, in such a high degree, that 

 even an economic coefficient of 30 per cent., nay, 50 per cent., and 

 even more, seems to be theoretically possible. 



Supposing we have to deal with a Carnot's cycle, the theoretical 



m m 



maximum Q of the mechanical effect is Q = Q l - , where Q 



li 



stands for the whole quantity of heat, which from the absolute 

 temperature TI is sinking down as far as T 2 . Taking T 2 = 273 

 + 37 = 310, the mechanical effect might at T x = 410 amount to 

 25 per cent., when the temperature 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 value only. For 

 it is ever an infinitesimal part only of the muscular mass that is 

 exposed to these high temperatures. At a small distance from these 

 furnaces of heat the temperature must have fallen so low as to be 



