243 



furnish all the water exhaled, ought first to be clear- 

 ly proved. The daily loss of weight which the whole 

 body experiences by the escape of perspirable matter, 

 is estimated by Haller at about 60 oz. in the warmer 

 climates, and from 56 to 30 in more temperate 

 climes *. Of this latter quantity, Dr Hales calcu- 

 lated the loss by the pulmonary exhalation to be 

 about 6 oz. f ; kvt the more accurate trials of Lavoi- 

 sier and Seguin make it to amount to about one-third 

 of the whole. The mean loss sustained by perspira- 

 tion was, according to them, 2 Ib. 13 oz., of which 

 the pulmonary discharge was 15 oz. and the cuta- 

 neous 1 Ib. 14 oz. J. When, therefore, we bear in 

 mind, that the surface of the bronchial cells is ten 

 times greater (114.) than that of the external skin, 

 and is, like it, duly furnished with exhalent vessels, 

 we are so far from seeing the necessity of resorting 

 to the supposition that water is formed chemically 

 in the lungs, that we can more readily imagine the 

 pulmonary exhalation to be rated in these estimates 

 below \vhat the extent of its exhalent surface may 

 be considered able to supply. 



198. Rejecting, therefore, the opinirn, that any 

 water is formed by the chemical union of oxygen 

 and hydrogen in the lungs or blood-vessels, it is not 

 within our plan (which professes to treat only of the 

 phenomena which arise out of the changes the air 

 suffers) to inquire farther into the laws of its pro- 



* Elements Physio!, torn. v. p. 58, 

 i Vegetable Statics, vol. i. p, 10, 

 Mem. de PA cad. 1790. 



