412 RESPIRATION. [CHAP.XXIX. 



in a state of chemical combination, we should not have been able 

 to obtain evidence of its presence by this process. Besides much 

 carbonic acid, oxygen, and a little nitrogen, are held in solution in 

 blood. 



With reference to the oxygen, it cannot be doubted that part is 

 in chemical combination with the constituents of the blood cor- 

 puscle, and part in a state of simple solution. 



The chief agents in effecting the absorption of gases in the blood 

 are undoubtedly the blood corpuscles, for it has been clearly proved 

 by Davy and others, that defibrinated blood possesses the power of 

 absorbing gases in a greater degree than blood serum. Magnus 

 found that blood was capable of absorbing 1^ times its volume of 

 carbonic acid gas. 



From the researches of Professor Lehmann upon the crys- 

 tallizable contents of the blood corpuscle, originally discovered by 

 Otto Fuuke, we are led to conclude that the colouring matter 

 of the blood is chemically affected by oxygen and carbonic acid 

 gases. 



Lehmann has shown, that if oxygen is allowed to pass through 

 defibrinated blood slowly for fifteen minutes, and is followed 

 the transmission of a current of carbonic acid for five minutes 

 under the influence of light, these crystals are formed in larger 

 quantity, and more rapidly, than if the carbonic acid is passed 

 through the blood first. These crystals are composed of a definite 

 chemical compound ; and there can be little doubt that the influ- 

 ence which the gases exert upon its crystallizing properties are of 

 a chemical nature.* 



It was formerly supposed that the oxygen of the air combined 

 with the carbon of the venous blood in the pulmonary capillari( 

 and that the carbonic acid eliminated from the system was forme< 

 at the pulmonary surface ; but later researches have shown, that 

 this gas exists pre-formed in the blood, and is therefore only 

 exhaled from the fluid contained in the vessels of the lungs, a view 

 which was first advocated by Lagrange and Hassenfratz in 1791. 

 It has been found that animals will give up carbonic acid when 

 placed in atmospheres which do not contain any oxygen, a fact 

 which could not be accounted for upon the supposition that this 

 gas was formed by the combination taking place in the pulmonary 

 organs. Again, the presence of both free oxygen and carbonic acid 



* For much interesting matter upon the subject of blood-crystallization, 

 the reader is referred to Lehmann's "Physiological Chemistry," 1853, trans- 

 lated by Dr. Day, Cavendish Society, vol.iii. 



