THE BLOOD. 91 



absorbed from the alimentary canal, this blood appears to be deficient in 

 solid matters, especially in colored corpuscles, owing to dilution by the 

 quantity of water absorbed, to contain an excess of proteid matter, and 

 to yielof 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 preteids. The 

 fibrin obtainable 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 of colored 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 

 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 vein; but that 

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

 constant element, namely, grape-sugar, which is found, whether saccha- 

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



Development of the Blood-Corpuscles. 



The first formed blood-corpuscles of the human embryo differ much 

 in their general characters from those which belong to the later periods 



FIG. 83. Part of the network of developing blood-vessels in the vascular area of a guinea-pig. 

 bl, blood-corpuscles becoming free in an enlarged and hollowed out part of the network ; a, process 

 of protoplasm. (E. A. Schafer.) 



of intra-uterine, and to all periods of extra-uterine life. Their manner 

 of origin is at first very simple. 



Surrounding the early embryo is a circular area, called the vascular 

 area, in which the first rudiments of the blood-vessels and blood-corpus- 

 cles are developed. Hare the nucleated embryonal cells of the inesoblast, 

 from which the blood-vessels and corpuscles are to be formed, send out 

 processes in various directions, and these joining together, form an irreg- 



