166 HANDBOOK OF PHYSIOLOGY. 



tion of a certain quantity of its oxy-haemoglobin, and its consequent 

 reduction to the purple variety (Deoxidized, or purple haemoglobin). 



(b.) Arterial blood coagulates somewhat more quickly. 



(c.) Arterial blood contains more oxygen than venous, and less car- 

 bonic acid. 



Some of the veins contain blood which differs from the ordinary 

 standard considerably. These are the Portal, the Hepatic, and the 

 Splenic veins. 



Portal vein. The blood which the portal vein conveys to the liver 

 is supplied from two chief sources; namely, from the gastric and mes- 

 enteric veins, which contain the soluble elements of food absorbed from 

 the stomach and intestines during digestion, and from the splenic vein; 

 it must, therefore, combine the qualities of the blood from each of these 

 sources. 



The blood, in the gastric and mesenteric veins will vary much ac- 

 cording to the stage of digestion and the nature of the food taken, and 

 can therefore be seldom exactly the same. Speaking generally, and 

 without considering the sugar, and other soluble matters which may 

 have been absorbed from the alimentary canal, this blood appears to be 

 deficient in solid matters, especially in colored corpuscles, owing to di- 

 lution by the quantity of water absorbed, to contain an excess of proteid 

 matter, and to yield a less tenacious kind of fibrin than that of blood 

 generally. 



The blood from the splenic vein is generally deficient in colored cor- 

 puscles, and contains an unusually large proportion of proteids. The 

 fibrin obtainable from the blood seems to vary in relative amount, but 

 to be almost always above the average. The proportion of colorless cor- 

 puscles is also unusually large. The whole quantity of solid matter is 

 decreased, the diminution appearing to be of colored corpuscles. The 

 plasma is said to be colored in consequence of its containing dissolved 

 haematin. 



The blood of the portal vein, combining the peculiarities of its two 

 factors, the splenic and mesenteric venous blood, is usually of lower 

 specific gravity than blood generally, is more watery, contains fewer 

 colored corpuscles, more proteids, and yields a less firm clot than that 

 yielded by other blood, owing to the deficient tenacity of its fibrin. 



Guarding (by ligature of the portal vein) against the possibility of 

 an error in the analysis from regurgitation of hepatic blood into the 

 portal vein, recent observers have determined that hepatic venous blood 

 contains less water, proteids, and salts than the blood of the portal 

 veins; but that it yields a much larger amount of extractive matter, 

 in which is one constant element, namely, grape-sugar, which is found, 

 whether saccharine or farinaceous matter has been present in the food 

 or not. 



