492 RESPIRATION. 



pie. Regnault and Eeiset 1 exposed dogs and rabbits for 

 many hours to an atmosphere containing 23 parts per 100 of 

 carbonic acid artificially introduced, and 30 to 40 parts of 

 oxygen, without any ill effects. They took care, however, 

 to keep up a constant supply of oxygen. These experiments 

 are at variance with the results obtained by others, but Re- 

 gnault and Reiset explain this difference by the supposition 

 that the gases in other observations were probably impure, 

 containing a little chlorine or carbonic oxide. There is no 

 reason to doubt, from the high Deputation of the observers 

 for skill and accuracy, that their experiments are perfectly 

 reliable ; and in that case, they prove that carbonic acid does 

 not act upon the system as a poison. This view is sustained 

 by the more recent observations of Dr. Hammond, which we 

 give in his own words : 



" I confined a sparrow under a large bell-glass, having 

 two openings. Through one of these I introduced every 

 hour 1,000 cubic inches of an atmosphere containing 45 parts 

 of oxygen, 30 of nitrogen, and 25 of carbonic acid, allowing 

 the vitiated air in which the animal had respired partially to 

 escape. At the end of twelve hours the bird was in as good 

 a condition as at the commencement of the experiment ; and 

 when the bell-glass was raised, it flew away as if nothing had 

 happened to it. A mouse subjected to a similar experiment 

 also suffered no inconvenience." 2 



In breathing in a confined space, the distress and finally 

 fatal results are produced, in all probability, more from animal 

 emanations and deficiency of oxygen, than from the presence 

 of carbonic acid. When the latter gas is removed as fast as 

 it is produced, the effects of diminution in the proportion of 

 oxygen are soon very marked, and progressively increase till 

 death occurs. Bernard has shown that birds enclosed in a 

 confined space, from which the carbonic acid is carefully 



1 Loc. cit. 



3 HAMMOND, Treatise on Hygiene, Philadelphia, 1863, p. 351. 



