160 BESPIRATIOK 



Schoffer, in 1860, demonstrated the remarkable fact that the presence of the red blood- 

 corpuscles greatly facilitates the extraction of carbonic acid from the blood, showing 

 that much more carbonic acid could be extracted, by means of a vacuum, from the entire 

 blood than from blood-serum. These observations were confirmed, in 1864, by Preyer 

 and by Pfliiger, who regarded the blood-corpuscles as playing the part of a feeble acid in 

 the process of extraction of carbonic acid. The researches of Preyer, in 1866, show 

 that carbonic acid is extracted more easily from arterial than from venous blood ; and, as 

 a result of his observations, he concludes that it is the combination of oxygen with the 

 coloring matter of the blood which operates as an acid in the processes for the analysis 

 of the blood for carbonic acid. 



Nitrogen of the Blood. As far as is known, nitrogen has no very important office in 

 the process of respiration. There is sometimes a slight exhalation of this gas by the 

 lungs, and analyses have demonstrated its existence in solution in the blood. Magnus 

 found generally a larger proportion in the arterial than in venous blood, although, in one 

 instance, there was a larger proportion in the venous blood. It is not absolutely certain 

 whether the nitrogen which exists in the blood be derived from the air or from the 

 tissues. Its almost constant exhalation in the expired air would lead to the supposition 

 that it is produced in small quantity in the system or supplied by the food. There is no 

 evidence that nitrogen enters into combination with the blood-corpuscles; it exists sim- 

 ply in solution in the blood, which is capable of absorbing about ten times as much as 

 pure water. Nothing is known with regard to the relations of the free nitrogen of the 

 blood to the processes of nutrition. 



Condition of the Gases in the Blood. It is now pretty generally admitted that the 

 oxygen of the blood exists, not in simple solution, but in a condition of feeble combina- 

 tion with certain of the constituents of the blood-corpuscles, particularly the coloring 

 matter. In studying the composition of the corpuscles, we have seen that, when air is 

 admitted to venous blood, oxygen unites with the hasmaglobine, forming oxyhsema- 

 globine. Carbonic oxide, which has a great affinity for the corpuscles, displaces almost 

 immediately all the oxygen which the blood contains. When the corpuscles are de- 

 stroyed, as they may be readily by receiving fresh blood into a quantity of pure water, 

 the red color is instantly changed to black. 



Carbonic acid is more easily exhaled from the blood than oxygen. It was this 

 principle which was obtained by those who first succeeded in extracting gas from the 

 blood. While there is every reason to suppose that oxygen is in combination with the 

 blood-corpuscles, carbonic acid seems to be in a condition of simple solution and is con- 

 tained more especially in the plasma. What may be considered as the free carbonic acid 

 of the blood behaves in all regards like a gas simply held in solution. The view that it is 

 held in solution chiefly in the plasma is sustained by the fact that serum will absorb 

 more carbonic acid than an equal volume of defibrinated blood. 



Liebig has shown that the phosphate of soda, one of the constituents of the blood, 

 influences to a remarkable degree the quantity of carbonic acid which can be held in 

 solution by any liquid. One hundredth of a part of this salt in pure water will double 

 its capacity for dissol\ 7 ing carbonic acid. When blood is in contact with a certain 

 quantity of air, oxygen is consumed and carbonic acid is exhaled. The fact that car- 

 bonic oxide, which has such a remarkable affinity for the corpuscles, displaces oxygen 

 almost exclusively, is another argument in favor of the view that the carbonic acid is 

 contained mainly in the plasma. 



The carbonic acid which is formed in the tissues and is taken up by the blood in its 

 passage through the capillaries exists in this fluid in two forms : one, in simple solution, 

 chiefly in the plasma, and the other, in a state of such loose chemical combination in 

 the bicarbonates that it may be disengaged by displacement by another gas and is 



