50 



THE ANIMAL AS A MACHINE, 



of the animal mechanism, to say nothing of its mental 

 part, are too complicated and obscure to permit at 

 present any very accurate statement of their nature, 

 methods, or results. 



16. The Efficiency of the Animal System, consid- 

 ered as a heat-engine — a probably incorrect assump- 

 tion — is very high as compared with the machines of that 

 class constructed by man. Helmholtz concluded from 

 the experiments of Hirn that the thermodynamic effi- 

 ciency of the system is about 0.20, confirming Hirn's 

 own earlier deduction that it is more efficient than the 

 steam-engine as ordinarily constructed. The fact, how- 

 ever, that the body is sensibly uniform in temperature 

 throughout, and that the more work done the more 

 rapid the circulation, and the more certain this uni- 

 formity of temperature, seem to prove it impossible 

 that such thermodynamic processes are carried on in 

 the animal system as are familiar to us in our heat- 

 engines, in which the maximum possible efficiency is 

 proportional to Carnot's function — range of temperature 

 divided by maximum absolute temperature. Whatever 

 its. method of operation, therefore, the animal machine 

 evades Carnot's law, and must illustrate some as yet 

 undiscovered process of energy-transformation. 



17. The Work of the Animal Machine is meas- 

 ured in horse-power " — a rate equivalent to 550 foot- 

 pounds per second, 33,000 per minute, 1,980,000 per 

 hour ; 75 kilogrammeters per second, 4500 per minute, 

 270,000 per hour, in British and metric measure respec- 

 tively ; the latter, however, being, as will be seen by 

 comparison, one seventieth less than the former. Its 

 measure may also be taken as a days work^ which may 

 have widely different dynamic values in different cases. 



