A STUDY OF THE CIRCULATION OF BLOOD 149 



spaces, and as the blood passes through the capillaries, part 

 of the plasma soaks out by osmosis and keeps these spaces 

 filled with a watery liquid known as the lymph (Latin 

 lymplia= water). Occasionally the colorless corpuscles work 

 their way by amoeboid motion out between the cells of the 

 capillary wall, and so escape into the lymph. 

 One might, therefore, say that the tissues 

 are bathed with lymph, which is really blood 

 minus the red corpuscles, and considerably 

 diluted ivith water. 



Changes in the Lymph. Since this liquid 

 is in immediate contact with the tissues, the 

 cells can take from it the nutrients necessary 

 for their growth and repair, and at the same 

 time can unload into the lymph their use- 

 less burden of waste matters. The lymph 

 in turn gives off some of these waste materi- 

 als to the blood and receives new supplies 

 of nutritive ingredients. In this way the 

 lymph acts as a middleman between the blood 

 and the tissues. By this constant inter- 

 change of materials the lymph in a given 

 organ is kept tolerably constant in its com- 

 position, but in different organs this liquid 

 varies considerably. 



The Lymphatics. The amount of lymph 

 is constantly increased by the osmosis that 

 goes on in the capillaries. Hence, if there 

 were no provision for draining lymph back 

 into the blood system, the tissues would become unduly dis- 

 tended. Such is the case in the condition known as dropsy. 

 This drainage is accomplished by a system of vessels known 

 as the lym-phat'ics. The lymphatics begin as extremely mi- 

 nute, thin-walled tubes, which open freely from the spaces 

 between the cells. As the tubes pass out through the tissues, 

 they unite to form larger vessels (see Fig. 57), and these 



FIG. 57. Lym- 

 phatics of the 

 Right Arm. 



g 



lymphatic 

 nodes. 



