CARBONIC ACID AND NITROGEN IN BLOOD. 59 



Preyer has objected to this view on the ground that blood is alkaline in reaction, 

 whilst all solutions that contain C0 2 in a state of absorption, or loose chemical 

 combination, are always acid. Pfltiger and Zuntz showed that blood, after being 

 completely saturated with C0 2 , still remains alkaline. 



As the bicarbonate only gives up its C0 2 very slowly in vacua, while blood gives 

 off its C0 2 very energetically, perhaps the soda, united with an albuminous body, 

 combines with the C0 2 and forms a complex compound, from which the C0 2 is 

 rapidly given off in vacuo. 



(3.) A minimal portion of the C0 2 may be chemically united in the 

 plasma with neutral sodic phosphate (Fernet). One equivalent of this 

 salt can fix 1 equivalent of C0 2 , so acid sodium phosphate and acid 

 sodium carbonate are formed, Na 2 HP0 4 + C0 2 + H 2 O = NaH 2 P0 4 

 + jSTaH,C0 3 (Hermann). When the gases are removed the C0 2 

 escapes, and neutral sodic phosphate remains. 



; It is probable, however, that almost all the sodic phosphate found in the blood- 

 ash arises from the burning of lecithin; we have, therefore, to consider only the 

 very small amount of this salt which occurs in the plasma (Hoppe-Seyler and 

 Sertoli). 



(B.) The C0 2 in the Blood-Corpuscles. The red corpuscles contain 

 C0 2 in a loose chemical combination; for (1.) a volume of blood can 

 fix nearly as much C0 2 as an equal volume of serum (Ludwig, Al. 

 Schmidt); and (2.) with increasing pressure the absorption of C0 2 by 

 blood takes place in a different ratio from what occurs with serum 

 (Pfliiger, Zuntz). The red corpuscles may fix more C0 2 than their 

 own volume, and the union of the C0 2 seems to depend upon the Hb, 

 for Setschenow found that, when Hb was acted on by C0 2 , its power 

 of fixing the latter was increased, which is perhaps due to the forma- 

 tion of some substance (paraglobulin) more suited for fixing C0 2 . 

 The colourless corpuscles also fix C0 2 after the manner of the serum- 

 constituents, and to the extent of to T V of the absorbing power of 

 serum (Setschenow). 



III. Nitrogen exists in the blood to the extent of 1'4 to T6 vol. 

 per cent., and it appears to be simply absorbed. 



It is still doubtful whether a small part of the N exists chemically united in the 

 red corpuscles. Outside the body when blood is heated, and when there is a free 

 supply of and warmth, it gives off very minute quantities of ammonia, which 

 are perhaps derived from the decomposition of some salt of ammonia as yet unknown 

 (Kiihne and Strauch). 



39. Arterial and Venous Blood. 



Arterial blood contains in solution all those substances which are 

 necessary for the nutrition of the tissues, those which are employed in 

 secretion; it also contains a rich supply of O. Venous blood must 



