506 



RESPIRATION 



physical condition. Thus, it will be seen that only a very small portion of the 

 carbon dioxid, namely, 5 per cent., behaves in accordance with the Henry-Dalton 

 law. 



In endeavoring to locate that portion of the carbon dioxid which is held in a 

 condition of both loose and stable combination, it should first be noted that the 

 serum and plasma contain sodium salts with which this gas could doubtlessly 

 unite. These salts are sodium carbonate and dibasic sodium phosphate. It 

 has been shown, however, that the quantity of available alkali which is combined 

 in the blood in the form of carbonates or phosphates, is not sufficiently large to 

 bind the amount of carbon dioxid normally present. For this reason, it must be 

 concluded that at least a part of this gas is held in a dissociable condition by 

 certain organic substances. 



If our attention is now directed to that portion of the carbon dioxid which is 

 united with the alkali of the blood, we are immediately confronted by the 

 difficulty that its quantity cannot be determined with accuracy and that even 

 that part of it which exists as bicarbonate, shows a most peculiar chemical be- 

 havior. Thus, defibrinated blood discharges all of its carbon dioxid with greatest 

 ease as soon as it is subjected to the vacuum pump, and even without the addition 

 of an acid to dissociate it from its bases. A bicarbonate solution, on the other 

 hand, possessing the concentration of the blood, liberates scarcely more than half 

 of its loosely bound carbon dioxid. If sodium bicarbonate is then added to whole 

 blood, all of its carbon dioxid can be obtained with the aid of the pump. To 

 these data should also be added the fact that the exposure of .plasma or serum 

 to the vacuum does not result in a complete liberation of the carbon dioxid. In 

 order to obtain it in its entirety, it is necessary to add an acid so that this so-called 

 "fixed carbon dioxid" may first be dissociated from its binder. While this point 

 has not been entirely cleared up as yet, it is doubtlessly true that the carbon 

 dioxid is contained chiefly in the plasma where it exists as sodium carbonate or 

 bicarbonate. A certain amount of it is also held in the corpuscles, in all probability 

 in combination with the sodium. 



With reference to the organic combinations of carbon dioxid, it should first 

 be stated that the most conspicuous of these is the loose union which this gas is 

 capable of forming with the hemoglobin. At this time, however, reference is had 

 solely to the alkali free portion of this pigment, namely, to its globin molecule. 

 If the hemoglobin content amounts to 15 per cent., and the carbon dioxid tension 

 to 30 mm. Hg, each 100 c.c. of blood contain 8.1 c.c. of this gas in combination 

 with the hemoglobin. In addition, it has previously been shown that 0.59 c.c. 

 are present in the physical state, which makes in all 8.7 c.c. We know, however, 

 that the total absorption of carbon dioxid by the red corpuscles at a tension of 30 

 mm. Hg amounts to about 14 c.c, and hence, it must be concluded that the re- 

 maining 5 c.c. are united with other constituents of these bodies, in all probability 

 with the alkali as bicarbonate and in a small measure also with the lecithin. It 

 has also been shown that the carbon dioxid is capable of forming certain unstable 

 compounds with the proteins of the plasma. As a general summary it might be 

 well to give the table compiled by Loewy^ which is based upon the fact that under a 

 pressure of 30 mm. Hg each 100 c.c. of arterial blood yield 40 c.c. of carbon dioxid. 

 This total quantity is distributed as follows : 



1 Handbuch der Biochemie, iv, 1908. 



