187 



from 70 to 100, never could obtain a single bub- 

 ble of air from his skin. These facts correspond 

 precisely with those already adduced concerning the 

 separation of air from water (45. 47.) by vegetable 

 bodies and other fibrous substances. They prove 

 decisively, that the human body, like other solid bo- 

 dies, has the power of separating the air naturally 

 contained in water : but that when the water con- 

 tains no air, none is separated by immersing the bo- 

 dy in it. It matters not what the substance is, says 

 Mr Hunter, if it be but warmer than the water ; 

 for a piece of iron heated to 150, and immersed in 

 water at 70, will cause the water to part with its 

 air ; but if the iron be ten degrees colder than the 

 water, little or no air will be separated *. The 

 small hairs distributed over the body facilitate, in all 

 probability, this separation of air ; for Mr Abernethy 

 observed, that, on introducing his hand and arm in- 

 to a jar of water at the temperature of .60, every 

 pore seemed covered with a little spherule of air, 

 which, on agitating the water, was detached, and 

 quickly rose to the top of the vessel ; and when the wa- 

 ter was changed at each repetition of the experiment, 

 a much greater quantity of air was collected, but in 

 moderately warm water he scarcely procured any 

 airf The air separated in experiments of this na- 

 ture was, according to Dr Priestley, just that mix- 

 ture of carbonic acid and partially vitiated air which 

 pump-water generally abounds with : and Dr Klapp, 



* On the Animal (Economy, p. 168. 

 f Essays, Surgical, &c. p. 115, 



