40 



THE ANIMAL AS A MACHINE. 



I 



the heart from the skin bring back colder blood from 

 that constantly refrigerated system of capillaries. The 

 mean temperature of the venous blood entering the 

 heart is about one degree warmer, in man, than the aver- 

 age for the whole system ; between one and two de- 

 grees warmer than the arterial blood. The tempera- 

 ture of the body, as a whole, is automatically regulated 

 by the system of nerves studied by Bernard ; which 

 causes the flow of blood toward any part to be accel- 

 erated when that part is cold, and retarded when it is 

 too warm. 



In every mechanism endowed with animal life, heat 

 is produced and work is performed. It by no means 

 follows that the work is the result of thermodynamic 

 transformation ; in fact, it seems impossible, in view of 

 the fact that we have in the animal system no differ- 

 ences of temperature such as characterize and limit the 

 action of the thermodynamic engine, that there should 

 be a thermodynamic transformation. The heat would 

 seem to be either a "by-product" or to be produced 

 simply to insure uniform and sufficient temperature to 

 permit the continuous and steady action of the vital 

 powers and the machinery of the body. All the ali- 

 mentary substances are combustible ; but it is not a 

 necessary consequence that they should be oxidized by 

 a heat-producing combustion within the animal system. 

 On the contrary, the quantity of heat which would be 

 thus produced, added to the quantity of work per- 

 formed by the vital organs, in digestion, nutrition, cir- 

 culation of the blood, — itself an enormous quantity, — 

 though reproducing the energy thus expended, as heat, 

 and thus, in one sense, costing nothing — and in brain- 

 work, to say nothing of wastes by conduction and 



