536 THE RESPIRATORY EXCHANGE 



is present in the red corpuscles in combination with alkali and 

 yields up some of this alkali, if the pressure of carbon dioxide be 

 high ; in this respect it resembles the proteids of the plasma. 



Bohr finds that haemoglobin can also absorb carbon dioxide ; 

 the combination is with the globulin portion, and thus is not 

 a. ected by the simultaneous combination of oxygen with the 

 iron portion of the molecule. The amount of carbon dioxide so 

 absorbed at a temperature of 38 and a pressure of 30 mm. is about 

 8 c.c. for the 14 or 15 grm. of haemoglobin which are contained 

 in 100 c.c. of blood. The remainder, apart from the small quantity 

 in solution, is probably combined with alkali as bicarbonate. 



These results must not be considered as rigidly representing 

 the condition in the blood circulating through the body, for the 

 blood acts as a whole, and according to the experiments of Zuntz 

 and Hamburger there is a constant exchange of salts between 

 the plasma and corpuscles, owing especially to the variations 

 which are occurring in the pressure of carbon dioxide. It is 

 probable that during coagulation the changes in the proteids of 

 the blood may alter the gaseous contents of the corpuscles and 

 of the fluid, which is no longer plasma but serum. 



The Nitrogen and Argon in Blood. The nitrogen in the 

 blood is about 1-2 volumes per cent., is chiefly in simple solution, 

 and thus follows Henry's law. Experiments by various observers 

 show that blood contains about 0*6 volumes per cent, more nitrogen 

 than water under similar conditions of temperature and pressure, 

 notwithstanding the fact that its coefficient of absorption is 

 smaller. This excess, according to Bohr, is due to some unknown 

 combination, which is formed in the presence of haemoglobin and 

 oxygen ; it does not depend upon the integrity of the red 

 corpuscles, for a similar excess is present in solutions of haemo- 

 globin crystals. 



As regards Argon, it is said that the venous blood received 

 directly from the living body contains 0-042 volumes per cent, of 

 this gas, a larger quantity than could be present in simple solution. 

 Blood which has been exposed to the air, and red corpuscles in 

 physiological saline, do not show any such excess. 



Further experiments upon these questions are needed. Accord- 

 ing to the balance of evidence at the present time, the nitrogen 

 and argon in the normal blood are considered as inert and of no 

 special physiological significance. It is necessary, however, to 



