d^ Agms Physiques sur l^ Vie. 151 



the resistance offered by their constitutions to the depressing 

 effects of a state of asphyxy while remaining submersed. 



Dr. Edwards next proceeds to inquire into the effects of 

 TRANSPIRATION. A liquid transfusion from the skin of 

 animals is constantly going on, either in the form of vapour 

 or of fluid in a denser state. 



The latter constitutes sweat. This phenomenon exhibits 

 great variations, and it is important to know what diminu- 

 tion of weight the body suffers in different circumstances. 

 In the course of an hour remarkable fluctuations occur. 



Dr. Edwards suspended frogs, toads, and salamanders, in 

 a calm air^ weighed them, and noted the results, which< 

 though very changeable in an hour, were generally uniform 

 in three, and in nine hours they averaged an equal result. 

 The successive diminution in the mass of fluids was evident. 



The results were modified by the alternate position of the 

 animals in a body of air in repose, or agitated by a draft* 

 And these results do not appear to depend upon any prin* 

 ciple of vitality, for they take place equally in death and in 

 life, and indeed among unorganized bodies, as, for example, 

 lumps of charcoal soaked in water. Therefore the cause of 

 the phenomenon of transpiration seems to be referribk 

 entirely to physical agents. The motion of the air seems to 

 be its exciting cause ; for even when^ to all appearance, it is 

 calm, it is in reality agitated more or less, and produces a 

 sensible evaporation from the skin. But the difference 

 between the effect of calm and agitated air is remarkable i 

 for in a draft, the animals exposed to it sweated away double 

 the quantity of liquid compared with those confined in a 

 room shut up. The amount lost was proportioned to the 

 intensity of the wind, and reached a triple amount over thosd 

 animals in stagnant air ; and this fact explains the variations 

 noticed from hour to hour among animals exposed to currents 

 of air. : 



The transpiration which occurs in very moist air, always 

 amounts to a diminution of weight ; but in dry air it is five 

 or ten times greater ; and when the influence of a moist state 

 of the atmosphere is compared with that of a dry state, the 

 amount of evaporation is equal to that of a dry and calm air» 



Transpiration may, therefore, be referred to the agitation 

 of the atmosphere for its exciting cause, beyond any modifii 

 cations of its density. And, although an elevated tempera- 

 ture be favourable to transpiration, its modifying influence 

 is less than that of other causes. 



In comparing the effects of absorption and transpirationi 



