242 



HUMAN PHYSIOLOGY 



scopic spaces of the tissues. Others have been led to the 

 view that they come from small sacs bounded by delicate 

 epithelium. But even if the latter conception is correct 

 we may continue to assume that matter derived from the 



active cells can find its way 

 along the lymphatics. The 

 fluid that comes from an or- 

 gan through the lymphatics 

 may be considered an over- 

 flow of plasma from the 

 blood-capillaries, modified 

 by the give and take of the 

 cells which it has bathed. 



The great majority of the 

 lymphatics contribute to one 

 chief channel. This is the 

 thoracic duct. It is formed 

 below the diaphragm by the 

 union of all the lymphatics 

 from the legs, the pelvis, the 

 abdomen, and viscera. The 

 lymph from the intestine is 

 at times laden with recently 

 absorbed fat. The duct is 

 continued up through the 

 thorax in front of the ver- 

 tebral column, receiving 

 branches from the chest, left 

 arm, and the left side of the 

 head. It empties at the junc- 

 tion of two great veins, one 

 bringing blood from the left 

 arm and one coming down 

 At the corresponding point 

 on the right there is a rather insignificant lymphatic 

 trunk through which comes the lymph from the right 

 arm and shoulder and the right side of the head. 



The thoracic duct in man is perhaps as large as a goose- 



FIG. 57. Lacteals and lym- 

 phatics during digestion. (Re- 

 drawn after Collins.) 



the left side of the neck. 



