744 Experiments 



tion of the oxygen or the two important excretions of urea and 

 carbonic acid. 



Pulmonary exchange. Let us speak first of the consumption of 

 oxygen and the production of carbonic acid, which are measured by 

 the same experiment. 



The experiments reported in Chapter I on birds which died in 

 confined and compressed air show that these two phenomena less- 

 ened in intensity during the compression. But it is not possible to 

 draw any conclusion, because the carbonic acid which is stored up 

 in the tissues of the animal adds its action to that of the oxygen, 

 and we shall see in Chapter VIII that carbonic acid also diminishes 

 the oxidations. 



As to the experiments reported in the present chapter, they can- 

 not furnish any information as to what takes place during the com- 

 pression. 



I therefore had to plan special experiments; unfortunately, the 

 problem presented more serious difficulties than one might have 

 supposed at first glance. 



In dealing with animals kept in closed vessels, as the idea was 

 to turn out, for the reason which has just been stated it was neces- 

 sary to eliminate the carbonic acid and keep to the measurement of 

 the oxygen consumed. Now under the influence of pressure, there 

 must be dissolved, in the very body of the animal, a certain 

 quantity of oxygen which it is impossible to estimate and subtract 

 from the total quantity of oxygen that has disappeared. 



That is not all. In the numerous experiments which I have tried 

 by this method, I took care always to act comparatively, to put 

 simultaneously two identical animals, one under a bell of known 

 capacity at normal pressure, the other in a compression receiver at 

 a determined pressure, with a potash solution which absorbed the 

 carbonic acid as it was formed. After a certain time had elapsed, 

 I analyzed the two airs, and I could easily determine the quantity 

 of oxygen absorbed by each of the two animals during a certain 

 unit of time. Unfortunately, the percentage analyses made neces- 

 sarily upon a small volume taken from the total mass of air in the 

 experiment have to be multiplied by this mass, to get the total con- 

 sumption, and the causes of error of either chemical or physiologi- 

 cal nature then assume a value so great that they exceeded the 

 differences noted between the two analyses. 



I therefore had to give up this type of experiment completely. 

 I used two others, which are not subject to the same criticism. 



The first is a little indirect. It consists of comparing the quantity 



