BLOOD OF PORTAL VEIN. 97 



jdelds a less firm clot than that yielded by other blood, 

 owing to the deficient tenacity of its fibrin. These 

 characteristics of portal blood refer to the composition of 

 the blood itself, and have no reference to the extraneous 

 substances, such as the absorbed materials of the food, 

 which it may contain ; neither, indeed, has any complete 

 analysis of these been given. 



Comparative analyses of blood in the portal vein and 

 blood in the hepatic veins have also been frequently made, 

 with the view of determining the changes which this fluid 

 undergoes in its transit through the liver. Great diversity, 

 however, is observable in the analyses of these two kinds 

 of blood by different chemists. Part of this diversity is no 

 doubt attributable to the fact pointed out by Bernard, that 

 unless the portal vein is tied before the liver is removed 

 from the body, hepatic venous blood is very liable to 

 regurgitate into the portal vein, and thus vitiate the result 

 of the analysis. Guarding against this source of error, 

 recent observers seem to 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, according to 

 Bernard and others, is one constant element, namely, grape- 

 sugar, which is found equally the same, whether saccharine 

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



Besides the rather wide difference between the composi- 

 tion of the blood of these veins and of others, it must not be 

 forgotten that in its passage through every organ and tissue 

 of the body, the blood's composition must be varying con- 

 stantly, as each part takes from it or adds to it such matter 

 as it, roughly speaking, wishes either to have or to throw 

 away. Thus the blood of the renal vein has been proved 

 by experiment to contain less water than does the blood of 

 the artery, and doubtless its salts are diminished also. The 

 blood in the renal vein is said, moreover, by Bernard and 

 Brown-Sequard not to coagulate. 



