DIGESTION.] 



PHYSIOLOGY, 



119 



In most parts of the body we find, besides blood 

 capillaries, fine passages very much like capillaries, 

 except that they contain a colourless fluid instead of 

 blood, and do not branch off from any larger vessels 

 like arteries. They seem to start out of the part in 

 which they are found, like the roots of a plant in 

 the soil. But though unlike blood capillaries in not 

 branching off from larger trunks, they resemble capil- 

 laries in joining together to form larger trunks corre- 

 sponding to veins, and the colourless fluid flows from 

 the fine capillary channels towards these larger trunks. 

 This colourless fluid is called lymph ; it is very much 

 like blood without the red corpuscles, and the chan- 

 nels in which it flows are called lymphatics. 



The lymphatics from nearly all parts of the body 

 join at last into a great trunk called the thoracic 

 duct, which empties itself into the great veins of the 

 neck, as is shown in the diagram. Fig. 6, Z^., Zj., 

 Th, D, 



Now, many of the lymphatics start from the innu- 

 merable villi of the intestine, and are there called 

 lacteals (Fig. 6, Let,) \ so that lacteals may be said 

 to be those lymphatics which have their roots in the 

 villi of the intestine. 



But what has all this to do with the digestion of 

 fat? Lacteal means milky, and the lymphatics 

 coming from the villi are called lacteals because, when 

 digestion is going on, the fluid in them, instead of 

 being transparent as in the rest of the lymphatics, 

 is white and milky. Why is it thus white and 

 milky? Because it is crowded with minute particles 

 of fat, and those minute particles of fat come from 

 the inside of the intestine. They are the same 



