PROBLEM OF PHYSIOLOGICAL HEAT. 325 



selves, so as to occasion growth and the renewal of the worn- 

 out solid parts. 



If hence it follows that a general balance must be struck 

 in the organism between receipts and expenditure, or between 

 work done and wear and tear, it is unmistakably one of the 

 most important problems with which the physiologist has to 

 deal, to make himself as thoroughly acquainted as it is possi- 

 ble for him to be with the budget of the object of his exami- 

 nation. The wear and tear consists in the amount of matter 

 consumed ; the work done is the evolution of heat. This 

 latter effect, however, is of two kinds, inasmuch as the ani- 

 mal body evolves heat on the one hand directly in its own 

 interior, and distributes it by communication to the objects 

 immediately surrounding it; while, on the other hand, it 

 possesses, through its organs of motion, the power of produc- 

 ing heat mechanically by friction or in similar ways, even at 

 distant points. We now require to know 



Whether the heat directly evolved is ALONE to he laid to the 

 account of the process of combustion, or whether it is the SUM 

 of the heat evolved loth directly and indirectly that it is to be 

 taken into calculation. 



This is a question that touches the very foundations of sci- 

 ence ; and unless it receives a trustworthy answer, the healthy 

 development of the doctrine concerned is not possible. For 

 it has been already shown, by various examples, what are 

 the consequences of neglecting primary quantitative determi- 

 nations. No wit of man is able to furnish a substitute for 

 what nature offers. 



The physiological theory of combustion starts from the 

 fundamental proposition, that the quantity of heat which re- 

 sults from the combustion of a given substance is invariable 

 that is, that its amount is uninfluenced by the circumstances 

 which accompany the combustion ; whence we infer, " in spe- 

 cie" that the chemical effect of combustible matter can un- 

 dergo no alteration in amount even by the vital process, or 



