452 FRAGMENTS OF SCIENCE 



animal organism can also generate heat outside of itself. 

 A blacksmith, for example, by hammering can heat a nail, 

 and a savage by friction can warm wood to its point of 

 ignition. Now, unless we give up the physiological axiom 

 that the living body cannot create heat out of nothing, 

 "we are driven," says Mayer, "to the conclusion that it 

 is the total heat generated within and without that is to be 

 regarded as the true calorific effect of the matter oxidized 

 in the body." 



From this, again, he inferred that the heat generated 

 externally must stand in a fixed relation to the work ex- 

 pended in its production. For, supposing the organic 

 processes to remain the same; if it were possible, by the 

 mere alteration of the apparatus, to generate different 

 amounts of heat by the same amount of work, it would 

 follow that the oxidation of the same amount of material 

 would sometimes yield a less, sometimes a greater, quan- 

 tity of heat. "Hence," says Mayer, "that a fixed relation 

 subsists between heat and work is a postulate of the 

 physiological theory of combustion." 



This is the simple and natural account, given subse- 

 quently by Mayer himself, of the course of thought started 

 by his observation in Java. But the conviction once 

 formed, that an unalterable relation subsists between work 

 and heat, it was inevitable that Mayer should seek to ex- 

 press it numerically. It was also inevitable that a mind 

 like his, having raised itself to clearness on this important 

 point, should push forward to consider the relationship of 

 natural forces generally. At the beginning of 1842 his 

 work had made considerable progress; but he had become 

 physician to the town of Heilbronn, and the duties of his 

 profession limited the time which he could devote to 



