18 



THE COMPOSITION OF EXPIRED AIK. 



produce death is usually that required to jnoduoe the proportions of caibouic acid 

 and of o.xytreri indicated above, and, hence, is in proportion to the size of the jar. 

 A mouse should live about twice as long in a jar of 2000 c.c. as in one of 1000 c. c, 

 other conditions as to temperature, etc., being the same, and commencing with 

 ordinary atmospheric air. 



The duration of life in the e.\i)eriments witli atmospheric air in elo.sed vessels, 

 makiu'' due allowance for variations in the air volume, coincides quite closely with 

 the duration of life in the " Hammond " e.\periment. The air analyses at death of 

 the animals in the two forms of experiment, also gave very similar results. lu 

 comparing the results shown in Tables G and I, it is necessary to bear in mind the 

 differences in the size of the jars and in the weight of the animals used in the sev- 

 eral experiments. As a general rule, the animal dies when the carbonic acid has 

 increased to between 12 and l.". [m- cent, and the oxygen has diminished to be- 

 tween 5 and G per cent. Is death due to the increase in the carbonic acid, or to 

 the tliniimition in the oxygen, or to both ? 



Some data foi- answering this question are presented in Table L, which shows 

 the results obtained by placing animals in gaseous mixtures containing various pro- 

 portions of carbonic acid, oxygen, and nitrogen. The animals experimented on 

 were mice, rats, rabbits, guinea-pigs, and sparrows. Fi-om this table it will be seen 

 that the diminution in oxygen in the inspired air was the most important factor iu 

 pi-oducing death, and that so long as the oxygen is present in the proportion of 6 

 per cent, and upwards, carbonic acid may be present to the amount of 20 per cent, 

 without causing death. When the cai'bonic acid forms much more than 20 per 

 cent, of the mixture, say 30 to 40 per cent., the oxygen must form at least 12 per 

 cent, to preserve life. 



If the proportion of oxygen in the mixture be reduced, the duration of life is 

 shortened, as will be seen from the following extract from Table L : 



In these experiments the proportion of oxygen Avas reduced to about one-half of 

 that in the normal atmosphere, and the duration of life was also reduced about one- 



