43 



denoting the mean temperature are, necessarily, too high. 

 There are still very much wanted observations upon the 

 temperature of animals in cold climates. 



As in all these observations, the temperature of the 

 animal is very much above that of the air, it must neces- 

 sarily follow, that, to preserve this condition, there must be 

 an internal genesis of heat. In order to appreciate the 

 amount of heat thus produced, we must take into consider- 

 ation the cooling influences tending to reduce the tem- 

 perature of the heated body to that of the external air. Of 

 two bodies similarly constituted, and of nearly similar form, 

 raised to the same degree of heat above that of the external 

 air, the smaller must cool more rapidly than the larger, 

 because the proportion of its superficies to its mass is 

 greater, this being as the square of any of its linear dimen- 

 sions to the cube. An elephant, therefore, from this cause, 

 must cool more slowly than a mouse, its temperature with 

 the same genesis of heat ought, therefore, to be higher than 

 that of the mouse ; it is, however, actually lower. To 

 obviate the greater cooling of the mouse, therefore, it must 

 produce more heat. All animals throw off from the ex- 

 ternal and internal surfaces of their bodies a quantity of 

 water in the form of vapour. To raise the water into vapour 

 of the temperature of the heated body, there is required as 

 much heat as would raise that of the water 134°. All this heat 

 must be supplied by the animal, and, therefore, its abstraction 

 for this purpose must be a source of cooling of great im- 

 portance. Vierordt found, as a mean of many hundred 

 observations, that he threw off from the surface of his lungs, 

 alone, when in complete repose, about sixteen ounces of 

 water in the twenty-four hours. The amount of fluid 

 thrown off in the form of insensible perspiration, by the 

 sweat glands of the skin, has been variously estimated. 

 Seguin, whose experiments are of high authority, esti- 

 mates it as in the proportion of 11 to 7 of the pulmonary 



