igO BIOLOGICAL LECTURES. 



the principal condition for the transformation of heat into 

 mechanical work is satisfied, and, on account of the enormous 

 difference 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." 



The objection has been raised "that those high tempera- 

 tures must necessarily destroy the life of the muscle, since the 

 latter becomes rigid and dies, even at 50° C." But Engelmann 

 considers this objection is of small value. " For it is ever an 

 infinitesimal part only of the muscular mass that is exposed to 

 the high temperatures. At a small distance from these fur- 

 naces of heat the temperature must have fallen so low as to 

 be harmless. The muscle will no more be destroyed by stimu- 

 lation than a steamer will be destroyed by heating the furnaces. 

 The material of combustion only will be destroyed ; the whole 

 steamer as such remaining unharmed." 



How the heat thus generated by the thermogenic particles 

 of sarcoplasm becomes converted into mechanical energy of 

 contraction may be stated in a few words. It acts as a stimu- 

 lus (Reiz) to the contractile fibrils, which, under the influence 

 of a higher temperature, absorb watery liquids with avidity. 

 Production of heat, then, is the essential antecedent to the 

 contraction of the contractile fibrils, because it is through In- 

 creased temperature that contractile filaments are made to 

 absorb more watery substance, and therefore become shorter 

 and thicker. 



There is one point which ought to be kept in mind in apply- 

 ing this theory to the explanation of contractility in general, 

 and that is, we must not confound the conception of heat with 

 that of temperature. Heat is a definite thing, something objec- 

 tive ; temperature is a state, a mere condition of the body. 

 Burn ten pounds of coal, and warm ten gallons of water, and 

 we get a certain temperature of the water. Burn the same 

 amount of coal, and warm twenty gallons of water instead, and 

 we get a temperature of the water differing from the first. The 

 amount of heat developed in each case is the same, but the 

 temperatures of the water are different. We must not con- 

 clude, therefore, because a certain body is cold to our touch it 



