314 HAND-BOOK OF PHYSIOLOGY. 



similar effect may be produced through the vaso-motor centre in the 

 medulla and spinal cord. Thus, by means of a self-regulating apparatus, 

 the skin becomes the most important of the means by which the tempera- 

 ture of the body is regulated. 



In connection with loss of heat by the skin, reference has been made 

 to that which occurs both by radiation and conduction, and by evapora- 

 tion; and the subject of animal heat has been considered almost solely 

 with regard to the ordinary case of man living in a medium colder than 

 his body, and therefore losing heat in all the ways mentioned. The im- 

 portance of the means, however, adopted, so to speak, by the skin for regu- 

 lating the temperature of the body, will depend on the conditions by 

 which it is surrounded; an inverse proportion existing in most cases be- 

 tween the loss by radiation and conduction on the one hand, and by 

 evaporation on the other. Indeed, the small loss of heat by evaporation 

 in cold climates may go far to compensate for the greater loss by radia- 

 tion; as, on the other hand, the great amount of fluid evaporated in hot 

 air may remove nearly as much heat as is commonly lost by both radia- 

 tion and evaporation in ordinary temperatures; and thus, it is possible 

 that the quantities of heat required for the maintenance of a uniform 

 proper temperature in various climates and seasons are not so different 

 as they, at first thought, seem. 



Many examples may be given of the power which the body possesses of 

 resisting the effects of a high temperature, in virtue of evaporation from 

 the skin. Blagden and others supported a temperature varying between 

 198 211 F. (92 100 C.) in dry air for several minutes; and in a 

 subsequent experiment he remained eight minutes in a temperature of 

 260 F. (126-5* C.). "The workmen of Sir F. Chantrey were accustomed 

 to enter a furnace, in which his moulds were dried, whilst the floor was 

 red-hot and a thermometer in the air stood at 350 F. (177 '8 C.); and 

 Chabert, the fire-king, was in the habit of entering an oven the tempera- 

 ture of which was from 400 to 600 F." (205 315 C.) (Carpenter.) 



But such heats are not tolerable when the air is moist as well as hot, 

 so as to prevent evaporation from the body. 0. James states, that in the 

 vapor baths of Nero he was almost suffocated in a temperature of 112 F. 

 (44-5 C. ), while in the caves of Testaccio, in which the air is dry, he 

 wa,s but little incommoded by a temperature of 176 F. (80 C.). In 

 the former, evaporation from the skin was impossible; in the latter it was 

 abundant, and the layer of vapor which would rise from all the surface 

 of the body would, by its very slowly conducting power, defend it for a 

 time from the full action of the external heat. 



(The glandular apparatus, by which secretion of fluid from the skin is 

 effected, will be considered in the Section on the Skin.) 



The ways by which the skin may be rendered more efficient as a cool- 

 ing-apparatus, by exposure, by baths, and by other means which man 

 instinctively adopts for lowering his temperature when necessary, are too 

 well known to need more than to be mentioned. 



