192 



the oxygen gas of the air ; and this carbon we con- 

 ceive to be given out by its exhalent function. 



152. In vegetables, and in the inferior animals, it 

 has been shewn, that carbonic matter is yielded only 

 while the circulation of their fluids continues: and 

 there are some facts related by M. Jurine which ren- 

 der it very probable, that the same thing holds true 

 concerning the carbon which is furnished by the hu- 

 man skin. He found, that in given times, the great- 

 est quantity of carbonic acid was formed by the skin 

 of a person in the vigour of life, next by a boy of 

 ten years of age, and least of all by a man of 70 ; 

 and that its production depended much, likewise, on 

 the season of the year, and the vigour of the cuta- 

 neous organs. All these facts seem necessarily to fol- 

 low from the opinion that this carbonic matter is 

 truly an excretion, depending altogether on the dis- 

 tribution of the animal fluids, and subject to ail their 

 variations. Whether, as in other animals, the air is 

 no longer decomposed by the skin when the circu- 

 lation has wholly ceased, we have not the means of 

 deciding ; but the results of the foregoing experi- 

 ments of Jurine, lead us to suppose that such is ac- 

 tually the fact. Even at the period in which Mr 

 Cruickshank wrote, it is probable, that, had the 

 composition of carbonic acid been then determined, 

 he would have formed a similar opinion concerning 

 the source of the carbon : for, in referring to his 

 experiments, he observes, " that (admitting the 

 common theory of fixed air and phlogiston) some- 

 thing passed off with the vapour of insensible per- 

 spiration by the skin, which rendered air fixed, and 



