522 MAINTENANCE EXCHANGE AND GROWTH 



parison of different individuals the determination of the 

 maintenance metabolism will give different numerical values, 

 which will not harmonize well if we base our results on the 

 unit of body weight. It does not depend so much upon the 

 size of the body as upon the amount of active protoplasm in 

 particular. A strong muscular individual will consume 

 more energy than one of equal weight in whom the muscula- 

 ture is replaced by the dead weight of large fat deposits. 

 The surface development, however, as correctly recognized 

 by C. Bergmann about the middle of the past century, but 

 first actually proved by Eubner, is a matter of great impor- 

 tance in this connection. The larger the surface in compari- 

 son to the body mass the greater the heat elimination, ceteris 

 paribus; and the greater the heat loss, necessarily the 

 greater the heat production must be to maintain constancy 

 of body temperature. As small individuals, in proportion 

 to their body volume, have a greater extent of surface, they 

 necessarily produce proportionately a greater amount of 

 heat. It has been proved in many cases that while the ratio 

 between exchange and body weight is irregular, almost con- 

 stant figures are obtained if the amount of metabolism is 

 calculated in proportion to the unit of body surface. There- 

 fore there can be no question as to the importance of this 

 factor. Exclusive emphasis of this may, however, as in 

 case of any one-sided consideration, miss the mark. Eubner 

 himself proved that the difference between the exchange in 

 big and little guinea pigs is still evident if heat elimination 

 is excluded by providing a surrounding temperature of 30. 

 Moreover an analogous difference in the metabolism of cold- 

 blooded animals (fish), in which temperature regulation 

 does not enter at all, has been shown by Jolyet and Eegnard, 

 and by Knauthe. E. Voit found that maintenance exchange 

 in poorly nourished individuals decreases, independently of 

 the body surface, with loss in the volume of body protein. 



