J£> CHANGES PRODICED IS AIR BY RESPIRATION. 



Inordinary re- We are very much inclined to think, that in ordinary re* 

 STteiurned s P u * a ^ on > a great part of the air is returned unaltered, viz. 

 unahered. that contained in the fauces, in the trachea, and probably a 

 portion of that in the larger branches of the bronchia. If 

 this circumstance be not adverted to in experiments upon 

 small quantities of air, the results can never be correct. 

 There is even a considerable difference in the quality of the 

 first and last portions of a single inspiration. In some ex- 

 periments made with a view to this subject, a small quantity 

 pf the first portions, given off in a common and natural ex- 

 piration, was received in a vessel over mercury; on examina- 

 tion, it contained only 3*5 per cent carbonic acid; in other 

 experiments the first portions contain from three to five per 

 cent; while the general average appears by the 11th, 12th, 

 and 13th experiments, to be about eight. 

 204 cubic The operator, after rather more than a natural inspira- 



contained '095 ^ on > expiree} £04 cubic inches into the mercurial gasome- 

 of carbonic ter, making his utmost efforts to press as much as possible 

 .»«*«• out of the lungs. These contained 9*5 per cent of carbo- 



nic acid, Here we are to recollect, that these 204 cubic 

 inches contained the first, as well as the last portions; the 

 t]rst portions have been proved to contain only from three to 

 live per cent; consequently the last portions must contain 

 more than appears by the average ; that is, more than 9*5 

 per cent. 



It now appeared to us of consequence to ascertain exactly 

 what happened to a given volume of atmospheric air, when 

 it was inspired and expired as often as possible. 



Fourteenth Experiment*, 



J4th cxperi- Three hundred cubic inches of atmospheric air were ad- 



■ . ent * 4 .. mitted into the mercurial gasometer G 1 ; tjie other, G 2, 

 Air repeatedly - °. j j xi ' 



respired. was empty. The nose being properly secured, and the 



mouth applied to the tube A, as usual, air was drawn from 



G 1, and by half turning the cock 2, was expired into, G 2, 



This was repeated until the contents of G 1 had been made 



to pass through the lungs, and transmitted to G 2. The 



* In this experiment there was obviously no occasion to make allow? 

 wee for the air contained in the tubes and sockets. We find its volume 

 to fce eighteen cubic inches, 



m 



