REGULATION OF EEAT IN MAN. 429 



it is born in such a state, as to require to be supplied with food by the 

 parent for some time, it is also more or less dependent up:>ja the warmth 

 imparted to it from the parental body. This is peculiarly the case with 

 the young of the Human species, which is longer dependent upon 

 parental aid, than that of any other animal. In the case of children 

 born very permaturely, the careful sustenance of their heat is one of 

 the points most to be attended to in rearing them ; and even the most 

 vigorous infants, born at the full time, are far from being able to keep 

 up their proper standard without assistance, if exposed to a cool atmo- 

 sphere. It has been ascertained that, during the first month of infant 

 life, the mortality in winter is nearly double that of summer, being 

 1-39 in January to 0-78 in July; and this striking difference cannot be 

 attributed to any other cause, than the injurious influence of 'external 

 cold, which the calorify ; ng powers of the infant do not enable it to 

 resist. As age advances, the power of generating heat increases, and 

 the body becomes much more independent of external vicissitudes ; so 

 that; in adult life, the winter mortality is to that of summer, only as 

 1-05 to 0-91, or less than one-sixth more. In advanced age, the calori- 

 fying power again diminishes ; and this we should anticipate from the 

 general torpor of the nutritive operations in old persons. Between 50 

 and 65 years of age, the relative winter and summer mortality are 

 nearly as in the first month of infancy ; and at 90 years, the average 

 mortality of winter is much more than twice that of summer, being as 

 1-58 to 0-64. 



767. It appears that there is a difference in calorifying power, not 

 merely at different ages, but at different seasons : the amount of heat 

 generated in summer not being sufficient, in many animals, to prevent 

 the body from being cooled down by prolonged exposure to a tempera- 

 ture, which is natural to them in winter. To what e.xtent this is the 

 case with Man, it is difficult to say. His constitution is distinguished 

 by its power of adapting itself to circumstances ; and he can live under 

 extremes of temperature more wide than those, which most other ani- 

 mals can endure ( 113). Whether in the torrid zone, or in the arctic 

 regions, he can maintain his healthy condition under favourable circum- 

 stances ; in each case his natural appetite leading him to the use of 

 that kind and amount of food, which is best suited to the wants of his 

 system. But the longer he has been habituated to a very warm or a 

 very cold climate, the more difficult he at first finds it to live comforta- 

 bly in one of an opposite character ; as his constitution, having become 

 adapted to one particular set of circumstances, requires time to accom- 

 modate itself to an opposite one. 



768. The means by which the heat of the body is prevented from 

 rising above its normal standard, even in the midst of a very high tem- 

 perature in the surrounding air, are of the most simple character. The 

 excreting action of the skin is directly stimulated by the application of 

 warmth to the surface ; and the fluid which is poured forth, being im- 

 mediately vaporized, converts a large quantity of sensible caloric into 

 latent, and thus keeps down the temperature of the skin. By this pro- 

 vision, the body may be exposed with impunity to dry air of 600 or 

 more, so long as the supply of fluid is maintained. But it cannot long 



