HEART AND BLOOD. 73 



combination, or medium compound of the two, precisely as 

 happens when wine is mixed with water and syrup. But when 

 a very minute quantity of chyle is mingled with a very large 

 quantity of circulating blood, a quantity of chyle that bears no 

 kind of proportion to the mass of blood, the effect is the same, 

 as Aristotle says, as when a drop of water is added to a cask of 

 wine, or the contrary ; the mass does not then present itself as 

 a mixture, but is still sensibly either wine or water. So in the 

 mesenteric veins of an animal we do not find either chyme or 

 chyle and blood, blended together or distinct, but only blood, 

 the same in colour, consistency, and other sensible properties, 

 as it appears in the veins generally. Still as there is a certain 

 though small and inappreciable proportion of chyle or uncon- 

 cocted matter mingled with this blood, nature has interposed 

 the liver, in whose meandering channels it suffers delay and 

 undergoes additional change, lest arriving prematurely and crude 

 at the heart, it should oppress the vital principle. Hence in 

 the embryo, there is almost no use for the liver, but the 

 umbilical vein passes directly through, a foramen or anastomosis 

 existing from the vena porta3, so that the blood returns from the 

 intestines of the foetus, not through the liver, but into the um- 

 bilical vein mentioned, and flows at once into the heart, mingled 

 with the natural blood which is returning from the placenta; 

 whence also it is that in the development of the foetus the liver 

 is one of the organs that is last formed; I have observed all 

 the members perfectly marked out in the human foetus, even 

 the genital organs, whilst there was yet scarcely any trace of 

 the liver. And indeed at the period when all the parts, like 

 the heart itself in the beginning, are still white, and save in the 

 veins there is no appearance of redness, you shall see nothing 

 in the seat of the liver but a shapeless collection, as it were, of 

 extravasated blood, which you might take for the effects of a 

 contusion or ruptured vein. 



But in the incubated egg there are, as it were, two umbilical 

 vessels, one from the albumen passing entire through the liver, 

 and going straight to the heart; another from the yelk, ending 

 in the vena portse; for it appears that the chick, in the first 

 instance, is entirely formed and nourished by the white; but 

 by the yelk after it has come to perfection and is excluded from 

 the shell ; for this part may still be found in the abdomen of 



