88 HAND-BOOK OF PHYSIOLOGY. 



stomach and intestines during digestion, and that in 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 accord- 

 ing 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, dextrin, and other soluble matters which may have 

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

 cient in solid matters, especially in red corpuscles, owing to dilution by the 

 quantity of water absorbed, to contain an excess of albumin, and to yield 

 a less tenacious kind of fibrin than that of blood generally. 



The blood from the splenic vein is generally deficient in red corpuscles, 

 and contains an unusually large proportion of proteids. The fibrin ob- 

 tainable from the blood seems to vary in 'relative amount, but to be almost 

 always above the average. The proportion of colorless corpuscles is also 

 unusually large. The whole quantity of solid matter is decreased, the 

 diminution appearing to be chiefly in the proportion of red corpuscles. 



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 red 

 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, albumen, and salts, than the blood of the portal vein; but that 

 it yields a much larger amount of extractive matter, in which is one con- 

 stant element, namely, grape-sugar, which is found, whether saccharine 

 or farinaceous matter have been present in the food or not. 



THE GASES OF THE BLOOD. 



The gases contained in the blood are Carbonic acid, Oxygen, and Nitro- 

 gen, 100 volumes of blood containing from 50 to 60 volumes of these gases 

 collectively. 



Arterial blood contains relatively more oxygen and less carbonic acid 

 than venous. But the absolute quantity of carbonic acid is in both kinds 

 of blood greater than that of the oxygen. 



Oxygen. Carbonic Acid. Nitrogen. 



Arterial Blood . . 20 vol. per cent. 39 vol. per cent. 1 to 2 vols. 

 Venous " 



(from muscles at rest) 8 to 12 " " " 46 " " " 1 to 2 vols. 



The Extraction of the Gases from the Blood. As the ordinary air- 

 pumps are not sufficiently powerful for the purpose, the extraction of the 

 gases from the blood is accomplished by means of a mercurial air-pump, 

 of which there are many varieties, those of Ludwig, Alvergnidt, Geissler, 

 and Sprengel being the chief. The principle of action in all is much the 





