

ARTERIAL AND VENOUS BLOOD. 45 



phosphate in the plasma (Fernet). One equivalent of this salt can fix one 

 equivalent of C0 2 , so acid sodium phosphate and acid sodium carbonate are formed, 

 Na 2 HP0 4 + C0 2 + H 2 - NaH 2 P0 4 + NaH,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 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 

 vrith serum (Pfliiger, Zuntz). The red corpuscles can 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 formation of some substance more suited for 

 fixing C0 2 . The colourless corpuscles, after the manner of the serum-constituents, 

 also fix C0 2 to the extent of ^ to T x of the absorbing power of serum. 



After the use of I, Hg, sodic oxalate, and nitrite, there is a diminution of C0 2 in arterial 

 blood (Feitelberg), and also in fever (Geppert, Minkowski). [In the last case it is perhaps clue 

 to the diminished akalinity, and this is in part owing to the acid products formed during 

 the decomposition of the tissues. ] 



III. Nitrogen exists in the blood to the extent of 1 4 to 1 *6 vol. per cent., and 

 it appears to be simply absorbed. 



. It is doubtful if any part of the N exists chemically united in the red corpuscles. Blood 

 warmed outside the body, and with a free supply of oxygen, gives off a minute quantity of 

 ammonia, which is 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, and it also contains a rich supply of O. Venous blood 

 must contain less of all these, but in addition it holds the used-up or effete 

 substances derived from the tissues, and the products of their retrogressive 

 metabolism are more numerous ; there is in venous blood a larger amount of C0 2 . 

 It is evident also that the blood of certain veins, the portal and hepatic, must have 

 special characters. 



The following are the most important points of difference between arterial blood 

 and venous blood : 



Arterial Blood contains 



more 0, 



less C0 2 , 

 more water, 

 more fibrin, 



less urea. 



It is bright red and not 



dichroic. 

 As a rule it is 1 C. warmer. 



more extractives, 



more salts, 



more sugar, 



fewer blood-corpuscles, 



The bright red colour of arterial blood depends on the presence of oxyhemo- 

 globin, whilst the dark colour of venous blood is due to its smaller proportion of 

 oxyhemoglobin, and the quantity of reduced haemoglobin which it contains. The 

 dark change of colour is not to be attributed to the larger quantity of C0 2 in 

 venous blood (Marchand) ; for if equal quantities of O be added to two portions of 

 blood, and if C0 2 be added to one of them, the colour is not changed (Pfliiger). 



[According to C. Schmidt, the blood of the portal vein contains more water, plasma, salts, 

 and fats, but less extractives and eorpuscles than the blood of the hepatic vein ; while (when 

 an animal is not digesting) sugar is absent or at least only in traces in the portal vein, and in 

 considerable amount in the hepatic vein ( 175).] 



40. QUANTITY OF BLOOD. In the adult the quantity of blood is equal to 

 Jy part of the body-weight (Bischqf), in newly-born children -^ ( WelcJcer). 



According to Schiicking, the amount of blood in a newly-born child depends to some extent 

 upon the time at which the umbilical cord is ligatured. The amount = T \ of the body- weight 



