98 PHYSIOLOGICAL CHEMISTRY. 



haemoglobin at -j- 18.4 C. and a pressure of 30 mm. 2.4 c. cm. carbon 

 dioxide are combined ; and since in the arterial blood nearly all the 

 haemoglobin exists as oxyhaemoglobin, it is difficult to obtain, at 

 least from the arterial blood, an appreciable fraction of the carbon 

 dioxide as carbon-dioxide haemoglobin. It cannot be denied that a 

 not insignificant part of the carbon dioxide of the blood is held by 

 the red corpuscles in loose combination ; but how this combination 

 takes place requires further investigation before it can be answered. 



The chief part of the carbon dioxide of the blood is found in the 

 blood-plasma or the blood-serum,, which follows from the fact that 

 the serum is richer in carbon dioxide than the correspond- 

 ing blood itself. By experiments with the air-pump on blood- 

 serum it has been found that the chief part of the carbon dioxide 

 contained in the serum is given off in a vacuum, while a smaller 

 part can only be pumped out after the addition of an acid. The 

 red corpuscles also act as an acid, and therefore in blood all the 

 carbon dioxide is expelled in vacua. A part of the carbon dioxide 

 is firmly chemically combined in the serum. 



Absorption experiments with blood-serum have shown us 

 further that the carbon dioxide which can be pumped out is in 

 great part loosely chemically combined, and from this loose combi- 

 nation of the carbon dioxide it necessarily follows that the serum 

 must also contain simply-absorbed carbon dioxide. For the form 

 of binding of the carbon dioxide contained in the serum or the 

 plasma we find the three following possibilities : 1. A part of the 

 carbon dioxide is simply absorbed; 2. Another part is loosely 

 chemically combined; and 3. A third part is in firm chemical 

 combination. 



The quantity of simply-absorbed carbon dioxide has not been 

 exactly determined. SETSCHEKOW considers the quantity in dog- 

 serum to be about -fa of the total quantity of carbon dioxide. 

 According to the tension of the carbon dioxide in the blood and its 

 absorption coefficient, the quantity seems to be still smaller. 



The quantity of firmly chemically combined carbon dioxide in 

 the blood-serum is the same as the quantity of simple alkali carbon- 

 ate in the serum. This quantity is not known, and it cannot be 

 determined either by the alkalinity found by titration, nor can it be 

 calculated from the excess of alkali found in the ash, because the 



