241 



result therefrom ; and that as insects and worms, by 

 means of their skins, preserve a superiority of tem- 

 perature over the medium in which they live, so 

 likewise those surfaces of the human body which 

 communicate directly with the air, derive from this 

 source a degree of heat also, by which means they 

 become, in some measure, auxiliary to the lungs *. 

 196. Besides this production of heat, as the prin- 

 cipal phenomenon arising from the change which 

 the air suffers in respiration, it has been supposed, 

 that water also is formed by an union of a portion of 

 the inspired oxygen gas with hydrogen residing in the 

 blood. But Mr Davy remarks, that there are no 

 reasons for supposing any residual atmospheric oxy- 

 gen to be immediately combined with fixed or na- 

 scent hydrogen, or hydro-carbonate, in the venal 

 blood at 98 ; and, consequently, none for believing 

 that water is immediately formed in respiration f ; 

 and Dr Bostock observes, that the discharge of hy- 

 drogen from the blood has been admitted without 



* This power in the skin to produce heat, naturally occurre4 

 to trie author from the view which he had taken of the effects 

 produced on the air by that organ. From information which he 

 has since obtained, he learns, that the same opinion was, many" 

 years ago, taught by Mr Allen in the lectures on physiology 

 which he delivered in Edinburgh j and a similar doctrine has been 

 pointed out to him in the " System of Chemical Knowledge" by 

 M. Fourcroy, where, however, it is obscured by the language of 

 that imperfect analogy which chemical physiologists never fail to 

 institute between respiration and combustion. 



f Researches, p. 423. 



Q 



