600 JOHN R. MURLIN 



heat must all pass through the surface it follows, other things equal, that 

 they will lose heat for any particular gradient of temperature in propor- 

 tion to surface. As applied to the animal body it is observed that, the body 

 temperature is nearly constant. Hence, if heat is lost in proportion to 

 surface, it must also be produced in proportion to surface. This im- 

 plies a causal relationship between surface loss and interior produc- 

 tion of heat. An elaborate biometric analysis proves nothing more re- 

 garding this causal relationship than is proved by the simple mathe- 

 matical analysis shown in Table 16. Whatever the physiological measure- 

 ment of surface, if it can be expressed even approximately by a formula 

 such as Meeh's it will follow that the ratio of body weights for certain 

 ranges will be the same as the ratio of body surfaces provided the weights 

 are not far apart, and for subjects of a continuous series in which weights 

 differ by small increments it will follow that surface will be only a little, 

 if any, better as a measure of metabolism than weight. 



The question of causal relationship, stands just where it always has 

 stood. If the possession of a large surface in proportion to weight, as in 

 a mouse, is accompanied by a vastly higher heat production per unit of 

 weight as compared with a horse, but the heat production is found to 

 be proportional to the surfaces in two such animals with approximately 

 the same body temperature, it seems to follow that surface loss of heat 

 is at least a more probable cause of heat production than body mass. The 

 same is true as between a baby and a man. 



On the basis of interpretation the objections to the law of surface run 

 in this way. Since the heat production of animals seems to be propor- 

 tional to surface area, it would seem to follow that heat is produced in 

 order to replace that which is lost, or to maintain body temperature. This 

 view, some say, denotes an all too nai've conception of nature. Blood does 

 not coagulate in order to prevent hemorrhage, but because certain chemical 

 agents are present with certain properties. The fact that it does stop 

 hemorrhage is quite incidental. It may have selective value, so that a 

 species whose blood did not -clot would have the worst of it in the struggle 

 for existence, but it will never do to say that thic chemical-physiological 

 function originated for the purpose of preventing hemorrhage; for that 

 would imply a mind at work in anticipation of the result. So also with 

 heat production. These critics, of whom Kassowitz(c) has been chief, pre- 

 fer to account for heat production in a perfectly causal manner. "Small 

 animals maintain a higher rate of oxidation, it is true, than large ones, but 

 this is not because they lose heat more rapidly in consequence of greater 

 (relative) surface, but because their alternating movements (later phases 

 caused reflexly by earlier phases) follow one another more rapidly on ac- 

 count of shorter nerve paths." Kassowitz(d) indeed finds that the higher 

 rate of oxidation in small, warm-blooded animals has even for them "dys- 

 teleological consequences ; for because of the more extensive muscular con- 



