RESPIRATION 239 



a solution of haemoglobin absorbs more of this gas than 

 water, and the quantity absorbed is not proportional to the 

 pressure. The haemoglobin of the corpuscles may therefore 

 hold a portion of the carbon dioxide in combination (Bohr)., 

 This cannot, however, be considered as settled. 



When blood is saturated with carbon dioxide and then 

 separated into serum and clot, the serum is found to yield 

 more gas than the clot ; but if the serum and clot are 

 separately saturated, the latter takes up more carbon dioxide 

 than the former. From this it is argued that a substance 

 combined with carbon dioxide must in blood saturated with 

 the gas pass out of the corpuscles into the serum. This 

 cannot be haemoglobin, for it remains in the corpuscles, but 

 it may very well be an alkali, combined with the carbon 

 dioxide and thus set free from its connection with the 

 haemoglobin. And, as a matter of fact, under the circum- 

 stances described, it has been found that alkalies do pass 

 from the clot into the serum (Zuntz), and chlorine from the 

 serum into the corpuscles (Lehmann), which at the same 

 time gain water and become larger. The molecular con- 

 centration (p. 360) of the serum of defibrinated blood, as 

 measured by the lowering of the freezing-point, increases 

 when it i? saturated with carbon dioxide. On the other 

 hand, when blood is saturated with oxygen, alkalies pass out 

 of the serum into the corpuscles, which at the same time lose 

 water and shrink in volume, while the molecular concentra- 

 tion of the serum is diminished. Hamburger has extended 

 these observations to the circulating blood, and has shown 

 that the plasma of venous blood has a higher percentage of 

 alkali, proteid, sugar and fat than the plasma of arterial blood, 

 and that the corpuscles have a greater volume, though not a 

 greater diameter. We may, therefore, suppose that in the 

 pulmonary capillaries, under the influence of oxygen, water 

 passes into the plasma from the corpuscles. In the systemic 

 capillaries the blood becomes loaded with carbon dioxide, 

 and therefore the corpuscles take up water from the plasma, 

 which accordingly has a more concentrated supply of food- 

 substances to offer to the tissues than the plasma of arterial 

 blood itself. Some writers see in this interchange an 



