THE LYAIPHATIC SYSTEM 



121 



comparable to the fluid part or plasma of the blood. While blood 

 is a carrier for both in-going and out-going materials of metabolism, 

 on account of being confined to the capillaries it is not brought into 

 direct contact with the tissue-cells of the body. The cells are, 

 however, bathed in tissue fluid, which can permeate the tissues by 

 diffusion. It contains cells of a type that can migrate through the 

 walls of vessels and when it enters the lymphatics it becomes lymph. 

 The lymph is thus a general medium of transmission with special 

 cell functions. The fat-carrying function of the intestinal lym- 

 phatics, in which the delivery of 

 food materials directly to the blood 

 is the principal consideration, is 

 doubtless a very special phase of 

 the transfer mechanism. 



The cell contents of lymph ves- 

 sels and spaces are amoeboid cells 

 or leucocytes (cf. p. 33). Leuco- 

 cytes of several kinds are found in 

 various situations in the body. 

 Since they are wandering cells, 

 their situation at any one time re- 

 veals little of their points of origin. 

 They are formed originally in lymph 

 nodes, in the spleen, in the bone 

 marrow, in endothelial linings, ar.d 

 by local proliferation of connective 

 tissue cells. They serve a variety 

 of purposes of which the phagocytic action, chiefly ingestion and 

 destruction of bacteria, and disintegration of erythrocytes and 

 other cell debris, is one of the chief. 



Lymph nodes, which, as just indicated, are centres for the 

 proliferation of certain types of leucocytes, concentration points 

 for such cells, and local centres of phagocytic action, appear to be 

 situated strategically with reference to parts of the body served. 

 In local infection, the activity of leucocytes of various kinds at 

 the point of injury can be correlated with that of leucocytes in the 

 nearest lymph nodes and the general relation can be observed in the 

 appearance and behaviour of the two regions themselves. The 



Fig. 68. Homologies of male (A) and 

 female (B) urinogenital systems: b, 

 urinary bladder; cc, crura clitoridis; cp, 

 crura penis; dd, ductus deferens; ep, 

 epididymis; k, kidney; ov, ovary;" r, 

 rectum; t, testis; tu, uterine tube; u, 

 urethra; ut, uterus; ur, ureter; va, 

 vagina; vs, seminal vesicle; vs', vesti- 

 bulum, urethra. 



