406 THE COMPOSITION OF EXPIRED AIR. 



with the products of respiration as it passed through the series, being 

 a repetition of the experiments of Brown-Sequard and d'Arsonval. 



In the great majority of cases, death was evidently due to the dimi- 

 nution in the oxygen and increase in the carbonic acid, the proportions 

 of these gases present in the jar when an animal died being that as 

 reported, i. e., the oxygen was reduced to between 4 and 6 per cent and 

 the carbonic acid increased to from 12 to 14 per cent. The mode of death 

 of the animals was similar to that observed in slow asphyxia, and the 

 results of careful post-mortem examination and microscopic investiga- 

 tion do not indicate the effects of any organic poison. 



The insertion of absorption tubes containing caustic alkalies between 

 the bell jars, to absorb the carbonic acid, and of concentrated sulphuric 

 acid, did not give results corresponding to those reported by Brown- 

 Sequard and d'Arsonval. 



The mice became habituated, to a certain extent at least, to the con- 

 ditions under which they were placed, and could live in an atmosphere 

 which was almost immediately fatal to a fresh mouse placed in it. This 

 had already been demonstrated by Bernard. In the case of seveial 

 mice, this power to resist the foul atmosphere was preserved for from 

 three to eight days after they had been removed from the jar, so that 

 they had a certain degree of permanent immunity. Experiments were 

 made to see if it was possible to develop such an immunity, and the 

 results obtained indicate such a possibility, but further investigation 

 will be necessary to settle this important point. At present it is uncer- 

 tain to what extent the immunity observed in a few mice was possessed 

 by them before they were experimented on, or was produced by their 

 first exposures to the vitiated atmospheres. 



From the data accumulated with reference to the composition of the 

 atmosphere in these bell jars by repeated analyses at short intervals, 

 compared with the results reported by Brown-Sequard and dArsonval, 

 it seems probable that the cases in which the last animal in the series 

 survived some of the others, and a low percentage of carbonic acid was 

 found in the jar, should be attributed entirely to defects either in 

 methods of air analyses or in the apparatus, or in both. If, however, 

 the life of the last animal was apparently saved by H 2 S0 4 in Dr. Ber- 

 gey's experiments, it was due to leakage in the connections from the 

 increased resistance caused by the interposition of the absorption tube. 

 This is an important fact, which is in direct opposition to the theory of 

 Brown-Sequard and d'Arsonval with regard to the influence of the 

 H 2 S0 4 in the absorption tubes. The great differences in individual 

 susceptibility of different animals must also be taken into account in 

 considering the results of these experiments. In some mice there 

 seems to be a very considerable immunity against the asphyxiating 

 effect of an atmosphere poor in oxygen and rich in carbonic acid. 



The duration of life of individual animals in experiments of this kind 

 depends upon the size of the bell jars in relation to the size of the 



