MOTION OF THE HEART AND BLOOD 



it is more comparable, as Aristotle says, to adding 

 a single drop of water to a cask of wine, or the 

 reverse. Then the total is not a mixture, but re- 

 mains either wine or water. So in dissecting the 

 mesenteric veins, chyme and blood are not found 

 either separately or mixed, but only the same blood 

 in color and consistency as appears in the other 

 veins. Still, since there is some chyle or uncon- 

 cocted material, however small, in this. Nature has 

 interposed the liver, in whose winding passages it 

 delays and undergoes more change, lest coming too 

 quickly in the rough to the heart, it suppress vitality. 



Hence there is almost no use for the liver in the 

 embryo. The umbilical vein clearly passes right 

 through the liver, with an opening or anastomosis 

 to the portal vein, so that fetal blood returning 

 from the intestines does not flow through the liver, 

 but mixed with maternal blood from the placenta 

 goes to the heart through this umbilical vein. So 

 in the development of the fetus, the liver is among 

 the last parts formed. In the human fetus we often 

 see all the organs fully marked out, even the genitals, 

 while there is still almost no trace of the liver. At 

 the time when all the organs, even the heart, appear 

 white, and there is no sign of redness anywhere ex- 

 cept in the veins, you will see nothing where the 

 liver should be except an irregular spot like blood 

 spilled out of a ruptured vein. 



In the developing egg there are two umbilical 

 veins, one passing through the liver directly to the 



[III] 



