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 

 contents 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 in- 

 gested, 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 constituents 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 relaxation of the fibers occurs, return of chyle into 

 the lacteal is prevented by a valve at the base of the villus. 



