306 



THE CIRCULATION 



outside in ways discussed in the latter part of the preceding chapter. 

 It is this abstracted part of the plasma, splitting off from the circulation 

 proper, which continually keeps up the lymph-flow. This is part, how- 

 ever, properly, of the hemolymph round from the ventricle to auricle 

 again. Let us examine into the forces which cause the plasma to split 

 away from the circulation proper and to pass as lymph so promptly 

 and in such large amounts (five liters daily at least) out of the capillaries 

 and into the veins by this indirect route of the tissue cell-spaces and the 

 lymphatics. 



FIG. 167 



k 



vaf-- 



Diagram of a lymph-gland or -node as seen in section: vef, efferent lymphatics; vaf, afferent 

 lymphatics; bg, blood-vessel; k, connective-tissue capsule; t, trabeculum; ad, adenoid tissue; v, 

 lymph-spaces; f, follicle (the essential tissue of the lymph-gland); n, reticulum. (B. Haller.) 



CAUSES OF THE LYMPH-FLOW. Four general causes of the lymph-flow 

 are apparent, and we may speak of them by these names: the pressure 

 from behind; the compression by muscles; the aspiration of the thorax; 

 and the muscular constriction of the lymphatic walls. Which of these is 

 the most important we do not know, and in the absence of this infor- 

 mation we may consider them in the order named. 



The cause of the immediate passage of blood-plasma out through the 

 capillary-wall into the lymph-spaces is doubtless a complex of several 

 forces, physical and physichemical. These we may denote as blood- 

 pressure and osmosis. 



