2 9 8 



COMPARATIVE ZOOLOGY 



In vertebrates only do we find a special absorbent sys- 

 tem. Three sets of vessels are concerned in the general 

 process by which fresh material is taken up and added 

 to the blood : Capillaries, Lacteals, and Lymphatics. 

 Only the two former draw material from the alimentary 

 canal. 



The food probably is absorbed almost as fast as 

 it is dissolved, and, therefore, there is a constant loss in 

 the passage down the canal. In the mouth and esoph- 

 agus, the absorption is slight ; but much of that which 

 has yielded to the gastric juice, with most of the water, 

 is greedily absorbed by the capillaries of the stomach, 

 and made to join the current of blood which is rushing 

 to the liver. Absorption by the capillaries also takes 

 place from the skin and lungs. Medicinal or poisonous 

 gases and liquids are readily introduced into the system 

 by these channels. 



We have seen that the oily part of the food passes 

 unchanged from the stomach into the small intestine, 



where, acted upon by the 

 pancreatic juice, it is cut 

 up into extremely minute 

 particles, and that the un- 

 digested albuminoids and 

 starches are digested in 

 the intestine. Two kinds 

 of absorbents are present 

 in the intestine, lacteals 

 and blood capillaries. Both 

 the lymphatic and blood 

 systems send vessels into 

 the velvety villi m with 

 which the - intestine is 

 lined. The blood capillaries lie toward the outside of 

 the villus and the lacteal in the center. The albumi- 



FIG. 257. Lacteal System of Mammal: a, 

 descending aorta, or principal artery; b, 

 thoracic duct; c, origin of lacteal vessels, 

 g, in the walls of the intestine, d; e, 

 mesentery, or membrane attaching the 

 intestine to walls of the body; /, lacteal, 

 or mesenteric, glands. 



