130 RESPIRATION. LECT. VI. 



volume. The newly introduced gas produces the increase 

 of weight of the whole, and counterbalances the diminution 

 arising from the increased volume. But, at the same time, 

 the film of water of the bubble certainly dissolves some car- 

 bonic acid, and in this way becomes heavier. I have tried 

 the effect of placing a carefully closed bladder, having very 

 thin sides, and filled with oxygen, in contact with carbonic 

 acid. Taking the precaution that the bladder was not moist, 

 the distention did not take place ; but after a certain time, 

 we found that the interchange between the two gases had 

 occurred, though the quantity of carbonic acid which was 

 introduced, did not exceed that of the oxygen which had 

 escaped. Lastly, I filled the lungs entirely with carbonic 

 acid, and in this state introduced them into oxygen ; they 

 collapsed, and the two gases mixed, but the volume of 

 oxygen introduced was less than that of the carbonic acid 

 which passed out. In all these cases, we must also con- 

 sider, besides the reciprocal action of the two gases through 

 the membrane, the presence of the water, which bathes the 

 membranes, water in which the carbonic acid is soluble. 

 The liquid acid thus formed is, on one side, in the presence 

 of a gas different to that which it holds in solution, and in 

 regard to which the free gas acts as in a vacuum. We 

 must, then, take into account the greater quantity of car- 

 bonic acid introduced into the soap bubble, or into the lungs, 

 by attributing it to a particular action of the two gases, such 

 as would constitute gaseous endosmose, and to an effect of 

 the gas at first dissolved, then exhaled. In order to clear 

 up this question, it is necessary to have recourse to gases 

 which have no affinity for water. 



Lastly, we must bear in mind the law discovered by 

 Graham of the diffusion of gases: the diffusiveness, or dif- 

 fusion-volume, of gases separated from each other by a 

 membrane, is inversely proportional to the square roots of 



