80 THE BLOOD. 



pears also to be 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 albumen, chiefly 

 in the form of alburninose, and yields 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 com- 

 position of the blood itself, and have no reference to the ex- 

 traneous 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 ob- 

 servable in the analyses of these two kinds of blood by dif- 

 ferent 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 seemed to have deter- 

 mined 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, accord- 

 ing to Bernard and others, is one constant element, namely, 

 grape-sugar, which is found, whether saccharine or farinaceous 

 matter have been present in the food or not. 



Besides the rather wide difference between the composition 

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

 gotten that in its passage through every organ and tissue of 

 the body, the blood's composition must be varying constantly, 

 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 experi- 

 ment 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. 



This then is an example of the change produced in the 

 blood by its passage through a special excretory organ. But 

 all parts of the body, bones, muscles, nerves, &c., must act on 

 the blood as it passes through them, and leave in it some mark 



