DIGESTION OF FOOD. 3845 
Our knowledge of the nature of the passage of the chyle 
from the intestines into the blood is now clearer than it was till 
recently, though still incomplete. 
The exact structure of a villus is to be carefully considered. 
If we assume that the muscular cells in its structure have a 
rhythmically contractile function, the blind terminal portion 
of the lacteal inclosed within the villus must, after being 
emptied, act as a suction-pump to some extent; at all events, 
the conditions as to pressure would be favorable to inflow of 
any material, especially fluid without the lacteal. The great 
difficulty hitherto was to understand how the fat found its 
Fic. 289.—Lymphatic vessels and glands (Sappey). 1, upper extremity of thoracic duct. pass- 
ing behind the internal jugular vein; 2. opening of thoracic duct into internal jugular and 
left subclavian vein. Lymphatic glands are seen in course of vessels. 
way through the villus into the blood, for, that most of it 
passes in this direction there is little doubt. 
It is now known that leucocytes (amceboids, phagocytes) 
migrate from within the villus outward, and may even reach 
its surface; that they take up (eat) fat-particles from the 
