214 Dr. W. Marcet. History of the Interchange of 



method proved unsatisfactory. Another experiment was made with 

 three bell-jars a small one, of a capacity of 10 litres, being placed 

 between two others which held, when full, 40 litres each; the three 

 bell-jars were connected with each other by india-rubber tubing 

 in the course of which an apparatus was disposed for the absorp- 

 tion of carbonic acid. The person under experiment breathed out 

 of and into the middle and smaller bell- jar, which held at the time 

 5 or 6 litres of air, while a known volume of air was driven from one 

 of the large bell- jars into the other, through the smaller receiver and 

 back again. The carbonic acid absorbed was replaced by oxygen 

 gas. The principle of the method was indeed the same as that 

 adopted by Regnault and Reiset, and more recently by Messrs. Jolyet, 

 Bergonie, and Sigalas.* Great difficulty, however, was met with in this 

 experiment, especially from the tension of gases in the bell- jars, and 

 it was ultimately given up. 



At last the simplest method was resorted to ; although, the results 

 of the experiments varying somewhat widely from each other, this 

 process necessitated the adoption of means. 



The experiments were conducted much on the same principle as 

 those made by C. Speck, every precaution being taken to carry them 

 out as correctly as possible. For this purpose, 40 litres of atmo- 

 spheric air were introduced into one of my bell-jars, the air being 

 saturated by passing it slowly through a glass vessel holding cotton- 

 wool wetted with tepid water. Air was inspired from this bell-jar 

 through the nose, with nose-pieces fitting closely into the nostrils, 

 and expired from the mouth into another bell- jar, also holding 

 40 litres; corrections were made for slight differences between the 

 bell- jars and for temperatures. In some of the experiments a valve 

 was placed in the tract of the air inspired, and in others no valve 

 was used, but the inspiratory and expiratory india-rubber tubes were 

 pinched alternately with the fingers to prevent any regurgitation. 

 Notwithstanding every care to breathe as naturally as possible, the 

 relations between the volumes of air inspired and expired were 

 occasionally found to differ widely from each other. On this account 

 it has been found necessary to reject a certain number of these experi- 

 ments, which yielded figures clearly far distant from those they should 

 have given ; and I have finally a series of ten experiments to record, 

 in which it will be observed that, although there is a very marked 

 difference between the figures obtained, still the means show that 

 nitrogen takes no appreciable part in the phenomenon of respiration, 

 if concerned at all in this function. 



The following are the results obtained, placed in a tabular form 



\ 



* References to these papers were given in my former communication. 



