THE SKIN A REGULATOR OF ANIMAL HEAT. 47 



it, even vegetables have a power of modifying their 

 own temperature, though in a much more limited 

 degree. Without this power of adaptation, it is ob- 

 vious that man must have been chained for life to 

 the climate which gave him birth, and even then 

 have suffered constantly from the change of sea- 

 sons ; whereas, by possessing it, he can enjoy life 

 in a temperature sufficiently cold to freeze mercury, 

 and is able, for a time, to sustain, unharmed, a heat 

 more than sufficient to boil water, or even to bake 

 meat. Witness the wintering of Captain Parry and 

 his companions in the Polar Regions ; and the ex- 

 periments of Blagden, Sir Joseph Banks, and others, 

 who remained for many minutes in a room heated 

 to 260, or about 50 above the temperature of boil- 

 ing water. The chief agents in this wonderful 

 adaptation of man to his external situation are un- 

 doubtedly the skin and the lungs, and in both the 

 power is intimately connected with the condition of 

 their respective exhalations : but it is of the skin 

 alone, as an agent in reducing animal heat, that we 

 have at present to speak. 



The sources of animal heat are not yet demon- 

 strably ascertained ; but that it is constantly gene- 

 rated and constantly expended has been lon known ; 

 and if any considerable disproportion occurs be- 

 tween these processes, it is at the immediate risk of 

 health. During repose, or passive exercise, the sur- 

 plus heat is readily carried off by the insensible per- 

 spiration from the lungs and skin, and by the contact 

 of the colder air ; but when the amount of heat 

 generated is increased, as during active exercise, an 

 increased expenditure becomes immediately neces- 

 sary : this is effected by the skin and lungs being 

 excited to higher action ; by the latter sending out 

 the respired air loaded with vapour, and the former 

 exhaling its fluid so rapidly as to form sweat. Ac- 

 cordingly, we find that in cold countries, and in frosty 

 weather, the superabundant heat being rapidly car* 



