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THE BEGINNINGS OF LIFE. 



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335 



interested. It "will be found quite harmonious with our 

 ordinary every- day experience, and should, therefore^ not 

 be very difficult for us to believe ^. An embryo of one of 



1 It is, moreover, not in the least at variance, as some seem to 

 suppose, with the facts at present known concerning the power which 

 some individuals have displayed of braving the influence of hot dry air for 

 very short periods^ either for the purposes of experiment or in Turkish 

 baths. When such comparisons are made, two points — frequently lost 

 sight of— should always be borne in mind. In the first place, there is 

 a very great difference between the destructive influence of hot dry air 

 and hot water ; and in the second place, highly organized warm-blooded 

 vertebrate animals are protected, as it were, from the destructive in- 

 fluence of hot dry air, for short periods, by certain counteracting 

 phenomena produced by the heat itself. On this subject, in one of 

 our recent and most valuable text-books on Physiology, Prof. Marshall 

 says : — ' The chief means of maintaining the normal temperature of 

 the body, in hot climates, consists in a large increase in the amount 

 of the water exhaled from the surface of the lungs and of the skin, 

 especially, however, from the latter. The skin becomes bathed 

 with fluid, the evaporation of which at the high temperature of the 

 surface and of the surrounding air, occasions a loss of heat and a 

 reduction in the temperature of the evaporating surface. The effect 

 in reducing the temperature of the body is greater if the atmosphere be 

 dry as well as warm, and then also if it be in motion : these conditions 



favour cutaneous exhalation and evaporation. 



The increased per- 



spiration excited by the great heat of the skin, furnishes, for a certain 

 time, sufficient material for evaporation. There is a limit, however, to 

 the amount of this excretion, and also to its rapidity of evaporation ; 

 for, when the surrounding air becomes moist, a check being put to the 

 evaporation, the body is no longer thus defended, and its temperature 

 begins to rise. Thus in a room, the temperature of which was 26o"F, 

 and the air dry, it was found possible to remain for eight minutes, 

 by which time the body was not much altered in temperature, although 

 the clothes and other articles in the room became very hot iBlagden 

 and Banks). A case is on record of a person remaining ten minutes 

 in a dry hot-air bath at 284^; whilst Chabert, the so-called fire-king, 

 weiit into ovens heated from 400"" to 600"" ; but, of course, for a ranch 



