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ELEANOR LINTON CLARK 



ent in the former regions and large saes or lakes in the latter. 

 The sacs always occur at a point where there are two conflicting 

 pressures. Because of the looseness of the subcutaneous tissue, 

 the lymphatic endothelium encounters little resistance from 

 without and expands in response to the increased pressure of 

 fluid within the vessels. At this stage the lymph heart first 



Fig. 9 Injections of the supra-scapular sac and of the posterior lymph sac 

 (lymph heart) in the same embryo (chick of 8^ days) showing comparative size. 

 S.S., supra-scapular sac; L.H., lymph heart. X 12.5. 



assumes a sac-like form. Since its muscular walls offer an 

 obstacle to its distension, it remains much smaller than certain 

 of the other sacs (fig. 9). 



OTHER FACTORS WHICH INFLUENCE THE LYMPH FLOW 



In addition to the differences in pressure at the various stages, 

 several other factors were noted, during the observations, which 

 influenced the flow of lymph in the superficial lymphatics. Many 

 of these have been mentioned casually in the description of the 

 different stages of the early lymph circulation. 



The lymph flow is influenced by the following factors: 



