AND ITS EFFECTS UPON ANIMAL LIFE. 51 



In order to ascertain whether an atmosphere which had served for respiration, once or oi'tener, 

 affected an animal differently from an atmosphere made up artificially from pure gases to the same 

 proportions as found in the analysis of the atmospheres in the different experiments reported on, a 

 series of experiments was undertaken to determine the effects of gaseous mixtures made up of 

 varying proportions of COj, O, and of N. The results obtained in this series of experiments are 

 shown in Table K, giving the capacity of the jar, the weight of the animal, the composition of the 

 atmosphere before and after the experiment, and the duration of life in such an atmosphere. The 

 construction of artificial atnios[)heres, and llic introduclion of an animal into such an atmosphere 

 without considerable alteration of the pro))ortions of the different gases, through the accidental 

 introduction of atmospheric air, was not always found an easy matter. The chief difficulty was 

 unfortunately a fundamental one, in that the CO, was not entirely free from atmospheric air ; the 

 oxygen contained more than lo per cent, of N ; while the attempt to obtain ]nire N from 

 atmospheric air by means usually employed for this purpose — burning out the O with 

 phosphorus — gave variable results with each attempt, the proportion of O remaining after the 

 absorption of the P3O5 usually ranged from 2 to 5 per cent. Under these circumstances it will be 

 seen that there was an almost insurmountable difificulty to the construction of an atmosphere having 

 the exact proportions of the different gases predetermined for it, and abundant evidence of this 

 difficulty was obtained from analyses of the mixtures after sufficient time had been allowed, as was 

 supposed, for the diffusion of the gases. 



The thorough diffusion of the components of gaseous mixtures appears to be a slow process. 

 Twenty four hours, or longer, was usually allowed for this to take place, yet from the variable 

 lengths of time during which animals of the same size and apparently possessing the same amount 

 of vitality could survive in atmospheres of equal volume made up from the same mixture, and the 

 variable projiortions of the different gases found on analysis after death of the animals exposed to 

 these atmospheres, show that perfect diffusion had not always taken place. These discrepancies 

 in the construction of the gaseous mixtures are to be regretted, though they are not great enough 

 to vitiate the value of the experiments taken as a whole. The positive character of the results is 

 too evident to allow these difficulties to have much weight. 



There is an uncertain feature in the determinations of the proportions of COj in the gaseous 

 mixtures, after death of the animal, in those instances where this gas was originally present in high 

 percentages. On this account it would be well to bear in mind that the third column representing 

 the proportions of the different gases present at death, marked N, represents, in fact, the gases 

 which failed to be absorbed in the gas-burette by the solutions of caustic soda and of pyrogallic 

 acid used to absorb the COj and O present. There is no doubt as to the presence of the propor- 

 tions of CO2, as stated in the different experiments, before placing the animal in the mixture. 

 Whether a large proportion of the CO^ was likewise absorbed by the animal, it is impossible to say. 

 There is no probability that such was the case. A part of the loss of CO, may also be accounted 

 for in the method employed in making the gaseous mixtures. These mixtures were made by 

 displacing water from the jars which were to contain them. The water may have taken uj) the 

 CO2 more readily than the other gases, especially where this was the first gas introduced into the 

 jar, and may, therefore, have been a slight source of variation in the composition of the mixture ; 

 yet, it seems, from analysis made just before placing the animal in the mixture, that the loss in 

 this manner was very small. The desired proportion of CO„ was usually present, even after 

 twenty-four hours had been allowed for diffusion to take place. 



Chart III. shows the results obtained in these experiments as to the relative duration of life 

 and the relative proportions of COj and of O at the beginning of the experiment, as well as at 

 death of the animal. In comparing this chart with Chart I., it must be remembered that in this 

 series of experiments the composition of the atmosphere was a different and variable one, while in 

 the series of experiments shown in Chart I., the composition of the atmosphere at the beginning of 

 the experiment was invariably the same— /.c, atmospheric air. This fact, along with the variations 

 in size of jar for different animals, explains the longer or shorter duration of life in this series of 

 experiments as compared with that presented in Chart I. The very important influences of these 



