CIRCULATION OF BLOOD AND OF LYMPH 



167 



larger streams, both on and away from its banks, the pebbles 

 continue to be wet with the rain, and the 

 tiny rills flow constantly to join the larger &>,, Lymph 

 current, until, at the foot of the hill, there glands 



will be, perhaps, a single large stream car- 

 rying all the water that has fallen in the 

 path. 



In a similar way the lymph collects, at 

 first in indefinite channels without walls, 

 but farther on in tubes with walls, which 

 are then called lymph vessels. Figure 92 

 shows the way in which these lymph ves- 

 sels originate, and Figure 93, which shows 

 their numbers in the superficial tissues of the 

 arm, only exemplifies the abundance with 

 which all parts of the body are supplied. 



What Becomes of the Lymph? Lymph 

 is primarily the liquid part of the blood 

 squeezed out of the capillaries. It must go 

 somewhere, for if it continued to accumu- 

 late, it would form pool-like masses among 

 the tissues. Sometimes lymph does gather 

 in certain spaces; e.g. the trouble called 

 water on the knee is caused by the accumu- 

 lation of lymph in that joint as the result 

 of an injury. Severe rubbing at any point 

 in the skin causes lymph to collect and 

 form a blister. A large gathering of lymph 

 produces the disease called dropsy. Ordina- 

 rily, however, lymph flows away as fast as it 

 appears. 



The lymph vessels coming from all parts 

 of the body finally unite into two large 

 trunks. Lymph from the lower part of 

 the body flows into the large thoracic duct (Figs. 65 and 94) 



FIG. 93. THS 

 LYMPH VESSELS 

 IN THE SUPERFI- 

 CIAL TISSUES OF 

 THE ARM 



