THE LYMPH AND LYMPHATIC SYSTEM 333 



The lymph is a clear, colourless fluid, with " cor- 

 puscles " — minute nucleated cells or particles of pro- 

 toplasm — floating in it. The liquid part is closely 

 similar in its properties and chemical constitution to the 

 liquid part of the blood. It, indeed, consists largely of 

 the liquid part of the blood which exudes from the 

 finest hair-like blood-vessels or capillaries as they 

 traverse the various tissues, and it is the chief business 

 of the " lymphatics " or lymph-holding vessels to return 

 this exuded liquid to the blood system, which they do 

 by joining — like the rivulets of a river system — to form 

 two large trunks which open into the great blood-holding 

 veins at the region where they approach the heart. The 

 total amount of lymph in the lymphatic system is difficult 

 to estimate, but it is larger in quantity than the blood in 

 the entire blood-vascular system. A large number of 

 the delicate vessels of the lymphatic system take their 

 origin just below the lining layer of the intestine, and 

 ramify through the transparent membrane, which holds 

 the coils of intestine together, and is called the mesentery. 

 The fatty or oily materials of food pass through the 

 lining " cells " of the intestinal wall into these " lacteal " 

 or milky lymphatics, and consequently in an animal 

 killed and examined after a meal, the fluid- in them 

 has a milky appearance, and renders this kind of 

 " lymphatics " visible. 



They were for this reason the first to be detected, and 

 were known even in ancient times to anatomists. The 

 milky fluid in them was called "the chyle." Its milky 

 appearance is due to the same cause as the white opaque 

 appearance of milk, namely, to the presence of an 

 immense number of excessively small particles of oil 

 (fat) and a certain proportion of larger globules of the 

 same nature. It was thus not difficult for the old 



