22 THE COMPOSITION OF EXPIRED AIR, 



III these experiments the aniinals were in au atmosjiliere of less pressure tlian 

 the external air, the diminution amountiui' usually to about 2 mm. of tnercury, but 

 there is no reason to su[)pose that this exerted any influence ufjou the results obtained. 



Experiments Nos. 17, IS, and I'J show that the mice bvcame habituated, to a 

 certain extent at least, to the conditions 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 ali'eady been demonstrated by Bernard (;j). In the case of several 

 mice, this power to resist the foul atmosphere was pieserved foi* from three to eight 

 days after they had been I'emoved from the jar, so that they had a certain degree 

 of permanent immunity (See experiment 18, C). Experiments Nos. 20 to 28 were 

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

 indicate such a possibility, but fnrthei- investigation will be necessary to settle this 

 important point. At present it is uncertain to what extent the immunity observed 

 in a few mice was possessed by them before they were experimented on, or was 

 produced b}' their first exposui'es to the vitiated atmospheres. 



From the data accunuilated with leference to the composition of the atmos- 

 phere in these bell jai-s by repeated analyses at short intei'vals, compared with the 

 results leported by Bi'own-Sc(puu'd and d'Arsonval, it seems probable that the cases 

 in which the last animal in the series survived some of the others, and a low per- 

 centage of caibonic acid was found in the jar, should be attiibuted entii'ely to de- 

 fects either in methods of air anal}ses or in the apparatus, or in both. If, however, 

 the life of the last animal was apparently saved by HgSO^ in Dr. Rergey's experi- 

 ments, it was due to leakatje in the connections from the increased resistance caused 

 by the interposition of the absorption tube. Tliis is an important fact, which is 

 in direct opposition to the theory of Brown-Scquard and d'Arsonval w-ith i-egai'd to 

 the influence of the Hg SO^ in the absorption tubes. The great differences in 

 individual susceptibility of diffeient animals must also be taken into account in 

 considering the results of these experiments; foi' example, in experiment No. 11, 

 spari'ow No. i died when the pei'centage of oxygen was 9.34, and that of carbonic 

 acid was only 2.79, while No. 5 lived until the percentage of oxygen was reduced 

 to 8.53. In some mice there seems to be a very consideralile immunity against the 

 asphyxiating effect of an atmosphere poor in oxygen and i ich in caibonic acid. 



The duration of life of individual animals in ex[>eriments of this kind depends 

 u[)i)n the size of the bell jars in I'elation to the size of the animal, nn the amount of 

 fresh air supplied, on conditions of temperature and moisture, and on individual 

 peculiarities of the animal — and it seems probable that variations in these factors 

 will account for the different results obtained by different experimenter.^*. The 

 symptoms in the animals which died were those of death by slow asphyxia. 



