62 THE CIRCULATION OF THE BLOOD 



have been demonstrated in the lymph of the thoracic duct "in 

 from four to seven minutes." 



Lymph and Chyle. It is scarcely necessary to refer to the 

 differences between these two fluids. Chyle is the intestinal 

 lymph during digestion. In the intervals of digestion the con- 

 tents of the lacteals do not differ materially from lymph in other 

 localities. Chyle has a whitish milky appearance due to the 

 presence of emulsified and saponified fats. Its specific gravity 

 naturally depends largely upon the amount of fat ingested, but 

 is always higher than that of ordinary lymph and lower than 

 that of blood. Not only is there more fat in the chyle than in 

 lymph, but the other solids are also increased. The proteid con- 

 stituents are considerably more abundant. For the most part 

 the higher specific gravity is explained by the absorption of solids 

 in solution from the alimentary canal. 



Chyle is forced out of the lacteals by contraction of the non- 

 striated muscle fibers which run along by the vessel. When re- 

 laxation of the fibers occurs, return of chyle into the lacteal is 

 prevented by a valve at the base of the villus. 



