the Diffusion of Gases. 257 



The heavy carbonic acid which these minute cells may contain, 

 is not merely exchanged for oxygen, but for a larger volume of 

 oxygen, in the proportion of the diffusion- volumes of carbonic 

 acid and oxygen, namely, 81 carbonic acid are replaced by 95 

 oxygen. The resistance to passage through the most minute 

 tubes, is overcome by the diffusion action, as in the case of the 

 pores of the stucco-plug, and there follows a tendency to accu- 

 mulation on the side originally occupied by the carbonic acid. 

 This accumulation is limited by the increased facility with which 

 the air-vessels can empty themselves mechanically of a portion of 

 their contents, from their distended state. 



In the law of diffusion of gases, we have, therefore, a singular 

 provision for the full and permanent inflation of the ultimate air- 

 cells of the lungs. 



But it is in the respiration of insects, that the operation of this 

 law will be most distinctly perceived. The minute air-tubes 

 accompanying the bloodvessels to every organ, and like them 

 ramifying till they cease to be visible under the most powerful 

 microscope, are kept distended during the most lively movements 

 of the little animals, and the necessary gaseous circulation main- 

 tained, wholly, we may presume, by the agency of diffusion. 



In regard to the terms of the law of diffusion : " The diffusion, 

 or spontaneous intermixture of two gases in contact, is effected 

 by an interchange in position of indefinitely minute volumes of the 

 gases" My experiments, published on a former occasion, on the 

 diffusion of mixed gases (Quarterly Journal of Science, Sept. 

 1829), afford the first demonstration of the fact, that diffusion 

 takes place between the ultimate particles of gases, and not be- 

 tween sensible masses, and therefore that diffusion cannot be the 

 result of accident. For, in the case of a mixture of two gases 

 escaping from a receiver into the atmosphere, by apertures of 

 0.12 and 0.07 inch in diameter, it was not so much of the mix- 

 ture which left the receiver in a given time, but a certain propor- 

 tion of each of the mixed gases, independently of the other, cor- 



