34 ON MAGNITUDE [ch. 



may well vary as the surface-area, that produced by oxidation 

 ought rather to vary as the bulk of the animal: one should vary 

 as the square and the other as the cube of the Hnear dimensions. 

 Therefore the ratio of loss to gain, hke that of surface to volume, 

 ought to increase as the size of the creature diminishes. Another 

 physiologist, Carl Bergmann*, took the case a step further. It was he, 

 by the way, whp first said that the real distinction was not between 

 warm-blooded and cold-blooded animals, but between those of 

 constant and those of variable temperature: and who coined the 

 terms homoeothermic and poecilothermic which we use today. He 

 was driven to the conclusion that the smaller animal does produce 

 more heat (per unit of mass) than the large one, in order to keep 

 pace with surface-loss; and that this extra heat-production means 

 more energy spent, more food consumed, more work donef. Sim- 

 plified as it thus was, the problem still perplexed the physiologists 

 for years after. The tissues of one mammal are much like those of 

 another. We can hardly imagine the muscles of a small mammal 

 to produce more heat {caeteris paribus) than those of a large ; and 

 we begin to wonder whether it be not nervous excitation, rather than 

 quahty of muscular tissue, which determines the rate of oxidation 

 and the output of heat. It is evident in certain cases, and may be 

 a general rule, that the smaller animals have the bigger brains; 

 "plus I'animal est petit," says M. Charles Richet, "plus il a des 

 echanges chimiques actifs, et plus son cerveau est volumineuxj." 

 That the smaller animal needs more food is. certain and obvious. 

 The amount of food and oxygen consumed by a small flying insect 

 is enormous; and bees and flies and hawkmoths and humming- 



* Carl Bergmann, Verhaltnisse der Warmeokonomie der Tiere zu ihrer Grosse, 

 Gottinger Studien, i, pp. 594-708, 1847 — a very original paper. 



t The metabolic activity of sundry mammals, per 24 hours, has been estimated 

 as follows : 



Weight (kilo.) Calories per kilo. 

 Guinea-pig 0-7 223 



Rabbit 2 58 



Man 70 33 



Horse 600 22 



Elephant 4000 13 



Whale 150000 circa 1-7 



J Ch. Richet, Recherches de calorimetrie. Arch, de Physiologie (3), vi, pp. 237-291, 

 450-497, 1885. Cf. also an interesting historical account by M. Elie le Breton, 

 Sur la notion de "masse protoplasmique active": i. Probl^mes poses par la 

 signification de la loi des surfaces, ibid. 1906, p. 606. 



