1891.] Formation of Carbonic Acid in Human Respiration. 59 



influence of food and when fasting, or at a period of four hours at 

 least from breakfast, when a desire for lunch was clearly felt. 



The results aimed at, although applying to man instead of animals, 

 were similar in kind to those obtained on animals by Messrs. Reg- 

 nault and Reiset,* and more recently by Messrs. Chapman and Bru- 

 backer, of Philadelphia.f Regnault and Reiset by their admirable 

 researches have paved the way to a correct history of the chemical 

 phenomena of respiration ; and Chapman and Brubacker, who have 

 repeated these experiments by a similar method, deserve much praise 

 for their laborious and interesting investigation, confirming, in a 

 marked degree, the results obtained by Regnault and Reiset. 



Rabbits being the subject of the experiments, Regnault and Reiset 

 obtained for the relation between the oxygen consumed and C0 2 

 produced a mean figure of O919 from six experiments ; with Messrs. 

 Chapman and Brubacker the corresponding result, also from rabbits, 

 was 0-90. 



These experiments were made by confining animals in a receiver 

 or bell -jar, and absorbing the C0 2 they produced with potassium 

 hydrate aided by mechanical means, while oxygen was supplied 

 automatically as fast as the C0 2 was absorbed, and as nearly as 

 possible in equal volumes. An examination of the figures expressing 

 the results obtained by Regnault and Reiset and the American 

 physiologists will show that the animals at the end of the experi- 

 ment had to breathe an atmosphere containing an excess of C0 2 , as 

 it was impossible to rid the air entirely of this gas. The proportion 

 of C0 2 present in the air at the close of the experiment occasionally 

 rose to 3 per cent, and higher, and this is a rather large contamina- 

 tion to allow of results being applied to natural breathing, considering 

 that atmospheric air contains only from 0'04 to O'l per cent. C0 2 . 



Moreover, the proportions of oxygen in the chamber at the end of 

 the experiments varied considerably, although always lower than the 

 corresponding proportion in atmospheric air. So that, towards the 

 end of the experiments, the animals were breathing air containing 

 an excess of C0 2 and a deficiency of O. 



There must be another difficulty to contend with in such kinds of 

 experiments, amounting to the impossibility of keeping the animals 

 quiet, and muscular action exerts, we know, a very positive influence 

 on the phenomena of respiration. 



In addition to the labours of Regnault and Reiset, and Chapman 

 and Brubacker, I have to quote the papers of Carl Speck, J and of 



* ' Annales de Chimie et de Physique,' 1849. 



t ' Proceedings of the Academy of Natural Sciences of Philadelphia,' January, 

 1891. 



" Experimented TJntersuchungeniiber den EinflussderNahrung auf SauerstofE- 

 verbrauch und Kohlensaureausscheidung des Menschen," von Carl Speck, ' Archiv 

 fur Pathologic,' 1874. 



