THE CARBON DIOXIDE IN BLOOD 535 



to form sodium carbonate, or with double that amount to form 

 sodium bicarbonate. This determination must be considered as 

 only approximate, for it will be shown later that the amount of 

 sodium carbonate in serum cannot be accurately determined, 

 owing to the combination of some of the alkali with proteids. 

 An examination of the dissociation of a solution of sodium 

 bicarbonate of the same strength as that of serum (Ol to 0'2 per 

 cent.) shows that it behaves quite differently to serum. Thus 

 Bohr found that at a temperature of 37 and a pressure of only 

 0-2 mm. three-fifths of the total gas capable of dissociation were 

 firmly combined ; the solution, moreover, is completely saturated 

 at a very low pressure of carbon dioxide, whereas serum, in 

 Jaquet's experiments, contained only 45*8 volumes per cent, of 

 that gas in chemical combination at a pressure of 14*8 mm. of 

 carbon dioxide. It is, therefore, maintained by Bohr that sodium 

 carbonate and sodium bicarbonate play a very small part in the 

 direct gaseous exchange. 



Evidence has accumulated to show that the carriers of carbon 

 dioxide must be sought in the proteids of the plasma and corpuscles. 

 The globulins can act as weak acids and form combinations with 

 the alkalies in blood, but from these combinations they are dis- 

 placed when the pressure of carbon dioxide is high. Loewy and 

 Zuntz have shown that the quantity of a diffusible alkali in serum 

 can be increased by the passage of a stream of carbon dioxide ; 

 carbonates are thus formed at the expense of the indiffusible com- 

 binations of proteids with alkali. The combinations will vary 

 according to the mass influence of the proteids of the blood and 

 the pressure of carbon dioxide ; when the latter is high the 

 globulin will be deprived of its alkali, but will regain it when the 

 pressure of carbon dioxide falls. In this way the alkalies of the 

 blood will be brought into play by the acid properties of the serum 

 albumin and serum globulin of the blood. 



It is now necessary to inquire whether the proteids of the 

 blood-corpuscles may not also play a part in the absorption of 

 carbon dioxide. The red corpuscles contain about one-third of 

 the total carbon dioxide in the blood, thus the corpuscles of 

 100 c.c. of arterial blood contain about 13 c.c. of that gas. Less 

 than 1 c.c. of this amount is in simple solution at the temperature 

 of the body. The haemoglobin acts as an acid, and in the vacuum 

 of a gas-pump will drive carbon dioxide out of carbonates ; it 



