EVOLUTION OF HEAT. 625 



fying process, appears equally certain. Its great efficacy in such cases seems 

 to depend upon the readiness with which it will be taken into the circulation 

 by a simple act of endosmotic imbibition, when the special Absorbent process, 

 dependent upon the peculiar powers of the cells of the villi ( 461), are in 

 abeyance. There is no other combustible fluid, whose miscibility and whose 

 density, relatively to that of the Blood, will permit of its rapid absorption by 

 the simple physical process adverted to. 1 



660. That the oxidation of certain components of the food or of the tissues 

 is the fundamental source of Animal Heat, is further indicated by the close 

 conformity which we everywhere find between the activity of the Respiratory 

 process and the amount of Heat which is generated and this not merely when 

 we compare different tribes of animals with each other, but also when we com- 

 pare the amount of oxygen absorbed and of carbonic acid exhaled by the same 

 individuals under different degrees of external temperature ( 564, a). For 

 we find that the system possesses within itself a regulating power, by which the 

 combustive process is augmented in activity when the cooling influence of the 

 surrounding medium is considerable, so that this influence is resisted ; whilst 

 the internal fire (so to speak) is slackened, whenever the temperature of the 

 outer air rises so much, as to render the same generation of heat no longer re- 

 quisite. The appetite for food, and especially for those particular forms of it 

 which best afford the combustive pabulum, varies in the same degree ; and thus, 

 when supplied with appropriate nutriment, Man is able to brave the severest 

 cold, without suffering any considerable depression in his bodily temperature. 

 It would seem that the Cutaneous Respiration, small as it is, promotes those 

 molecular changes on which the maintenance of Animal Heat depends ; for it 

 was found by MM. Becquerel and Breschet, 2 that when the hair of Rabbits was 

 shaved off, and a composition of glue, suet, and resin (forming a coating 

 impermeable to the air) was applied to the whole surface, the temperature 

 rapidly fell, notwithstanding the obstacle thus offered to the evaporation of the 

 sweat, whereby, it might be supposed, the temperature of the body would be 

 considerably elevated. In the first rabbit, which had a temperature of 100 

 before being shaved and plastered, it had fallen to 89 by the time the mate- 

 rial spread over him was dry. An hour after, the thermometer placed in the 

 same parts (the muscles of the thigh and chest) had descended to 76. In 

 another rabbit, prepared with more care, by the time that the plaster was dry, 

 the temperature of the body was not more than 5J above that of the surround- 

 ing medium, which was at that time 69 J; and in an hour after this, the ani- 

 mal died. These experiments place in a very striking point of view the im- 

 portance of the cutaneous surface as a respiratory organ, even in the higher 

 animals ; and they enable us to understand how, when the secreting power of 

 the lungs is nearly destroyed by disease, the heat of the body is kept up to its 

 natural standard by the action of the Skin. A valuable therapeutic indication, 

 also, is derivable from the knowledge which we thus gain, of the importance of 

 the cutaneous respiration ; for it leads us to perceive the desirableness of keep- 

 ing the skin moist, in those febrile diseases in which there are great heat and 

 dryness of the surface, since secretion cannot properly take place through a dry 

 membrane. Of the relief afforded by cold or tepid sponging in such cases, 

 experience has given ample evidence. 



661. It has been held that the Chemical theory of Calorification is insufficient 



1 The Author has stated the very striking results of observations which he has had the 

 opportunity of making upon this point, in his Prize Essay "On the Use and Abuse of 

 Alcoholic Liquors," % 215, Am. Ed, 



2 "Comptes Rendus," Oct., 1841. These experiments have been repeated and con- 

 firmed by Magendie ("Gazette Medicale," Dec. 6, 1843). 



40 



