ii THE THERMIC ECONOMY OF THE ORGANISM 63 



This table shows that the maximum difference between A and 

 B, that is between the calories estimated and found, amounts to 

 4*1 cal. per cent, while the minimum difference is O'l cal. per 

 cent. The average difference between A and B in all the investi- 

 gations made during rest is O'l cal. per cent ; in all those made 

 during muscular work 0'3 cal. per cent ; the total average, that 

 under the usual circumstances, when work alternates with rest, is 

 0'2 cal. per cent. These experimental results justify the con- 

 clusion that nutritive substances in the course of their combustion 

 within the organism develop the same amount of heat as when 

 burnt outside, a conclusion in harmony with the law of the 

 conservation of energy. They also prove that the quantity of 

 heat developed daily by the organism can be calculated with 

 sufficient accuracy from the data of the exchange of material, on 

 the basis of the average values (standard figures) given by Eubner 

 and Atwater and Benedict for the heat of combustion of the 

 three main groups of organic food substances. 



II. As regards the production of heat, vertebrates are divided 

 into two classes, those with an invariable and those with a variable 

 temperature. The former class, represented by mammals and 

 birds, were designated homoiothermic animals by Bergmann ; the 



