390 RESPIRATION. 



acquainted with all the physical laws which may come into play 

 in the interchange of gases in the lungs, our exposition of the 

 positive facts referring to the respiration sufficiently show that we 

 have nearly succeeded in tracing to their physical fundamental 

 requirements the individual sections into which the respiratory 

 process may be divided. The first attempt to determine the 

 physical law according to which the blood and the air interchange 

 their gases in the lungs was made by Valentin in conjunction with 

 Brunner, and conducted with equal intelligence and perseverance. 

 Valentin arrived at the result, that this interchange of gases corre- 

 sponds perfectly with the law of the diffusion of gases established 

 by Graham, and that consequently the oxygen and carbonic acid 

 are interchanged in an inverse ratio to the square roots of their 

 densities. As it does not fall within the limits of the present 

 work to enter into more diffuse theoretical expositions, we will 

 here content ourselves with briefly indicating the difficulties which 

 oppose the unconditional assumption of this theory. In the inter- 

 change between the gases of the blood and the air in the lungs, 

 we meet with external relations differing wholly from the con- 

 ditions under which Graham observed the interchange of gases 

 through a porous partition wall, and on which he based his law ; 

 after what has already been stated, it would appear almost super- 

 fluous to observe, that in respiration an absorbed gas is op- 

 posed to an elastic fluid gas, while in the process of diffusion both 

 gases must be in the elastic fluid state and under equal pressures, 

 which cannot be the case in the respiration. These and some 

 other points, which are opposed to the direct application of the 

 law of diffusion to the respiration, might perhaps be of less im- 

 portance if this interchange of carbonic acid and oxygen occurred 

 in the ratio required by the law of diffusion, that is to say, that 

 85*16 vols. of carbonic acid should be interchanged for every 

 100 vols. of oxygen. If this ratio very frequently exists during 

 an animal diet, we have nevertheless encountered numerous facts 

 in our previous observations which appear to be diametrically 

 opposed to this law; a law cannot, however, tolerate an excep- 

 tion, and when the latter can be shown to exist, the law is without 

 force. It seems to us at least that many of the facts which have 

 been proved beyond a doubt by the most recent investigations, 

 notwithstanding all the concessions which might be made in 

 favour of the peculiar animal relations, cannot be brought entirely 

 into harmony with Valentin's theory. 



Vierordt has described the interchange of gases on the inner 



