THE ANIMAL AS A MOTOR. 



39 



known ; the quantities of energy which may be ob- 

 tained by their perfect combustion to carbonic acid 

 and water are well ascertained, and it only remains to 

 determine the exact nature of the processes by which 

 it is possible to effect their combustion at the tempera- 

 ture of the animal system, and to utilize by transform- 

 ation the resulting power through those intermediate 

 forms of energy-change which remain as yet undis- 

 covered, and, in that sense, mysterious. We do not 

 yet know how to produce combustion at a temperature 

 of 98° Fahr., that at which combustion certainly does 

 occur in the human system ; or at the still lower tem- 

 peratures at which such chemical changes go on in the 

 bodies of cold-blooded creatures ; nor do we know how 

 to secure transformation of heat into mechanical and 

 other forms of energy without sensible change of tem- 

 perature and with high efficiency. In all our uses of 

 heat-engines the wastes are a much greater proportion 

 of the available energy than in any animal system, 

 except where, as in some cases of application of the 

 heat-energy of steam, for example, the wastes of the 

 engine are, as in the human body, utilized for heating 

 purposes. 



The muscles when doing work, and all the glands, 

 every organ, in fact, while performing its legitimate 

 function, is found to become warmer ; indicating the 

 final appearance of whatever form of energy may be 

 operating in the system in the form of heat. Heat is 

 produced, apparently, in all the organs of the body, but 

 in different degree, accordingly as their action is intense 

 or deliberate. Those veins which return blood from 

 working organs bring it back slightly warmer than the 

 average for the whole system ; those coming in toward 



