404 



THE COMPOSITION OF EXPIRED AIR, 



experiment, also gave very similar results. In comparing the results 

 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 several experiments. As a 

 general rule, the animal dies when the carbonic acid has increased to 

 between 12 and 13 per cent and the oxygen has diminished to between 

 5 aud 6 per cent. Is death due to the increase in the carbonic acid, or 

 to the diminution in the oxygen, or to both? 



Some data for answering this question are presented, showing the 

 results obtained by placing animals in gaseous mixtures containing 

 various proportions of carbonic acid, oxygen, and nitrogen. The ani- 

 mals experimented on were mice, rats, rabbits, guinea pigs, and spar- 

 rows. The diminution in oxygen in the inspired air was the most 

 important factor in producing death, and so long as the oxygen is pres- 

 ent in the proportion of 6 per cent and upward, carbonic acid may be 

 present to the amount of 20 per cent without causing death. When 

 the carbonic 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 table: 



No. 



Weight. 



At beginning of experiment. 



At end of experiment. 



Dura- 

 tion of 

 life. 



Capacity 

 of jar. 



CO. 



0. 



N. 



CO. 



0. 



N. 





Grams. 



Per cent 



Per cent- 



Per cent. 



Per cent. 



Per cent. 



Per cent. 



Hours. 



c. c. 



8 



18 







11.35 



88.65 



6.56 



4.14 



89.3 



3i 



2,280 



9 



15 







11 35 



88.65 



7.43 



3.58 



89 



' H 



2,280 



10 



17 







11.35 



88.65 



7.52 



3.16 



89.2 



H 



2,280 



In these experiments, the proportion of oxygen was reduced to about 

 one-half of that in the normal atmosphere, and the duration of life 

 was also reduced about one- half. 



The toleration which is acquired by an animal by prolonged sojourn 

 in an atmosphere which is gradually becoming richer in carbonic acid 

 and poorer in oxygen, makes it impossible to compare the results as to 

 duration of life in such experiments with the results of experiments 

 in which the animal is placed at once in an atmosphere containing 

 abnormal proportions of these gases, so far as the effects of increase of 

 carbonic acid and diminution of oxygen are concerned, but death does 

 not occur in atmospheres in which the carbonic acid does not exceed 

 10 per ceut unless the oxygen is reduced to below 7 per cent of the 

 mixture. 



A series of experiments was made by injecting into animals the iiuid 

 condensed from the air expired by healthy persons and by a man with 

 a tracheal fistula, from whom it was possible to obtain such fluid without 

 contamination from the exhalations from the mouth. The injections 



