10 Florence R. Sabin. 



4. Statement of the Arguments foe the Venous Origin of the 

 Lymphatic System. 



I shall now take up the proof of the theory that the lymphatic 

 system is derived from the venous system, and will subsequently 

 analyze the opposing theory, which, in its most recent from, is that 

 lymphatics grow on the addition of tissue spaces (Kampmeier 66 and 

 66a). 



The essential elements in the establishing of the venous origin of 

 the lymphatics have been (1) the proof that lymphatic capillaries 

 grow by the sprouting of their endothelial wall and not by the addition 

 or hollowing out of connective tissue spaces. This argument is known 

 as the method of growth by sprouting. (2) The proof that lym- 

 phatics gradually invade the body from center to periphery, establishing 

 the point of lymphatic and non-lymphatic zones. This means that 

 the main ducts grow as capillaries by the same method as the per- 

 ipheral capillaries. This argument is known as the one of lymphatic 

 and non-lymphatic zones. (3) That the original lymphatic ducts 

 bud off directly from the veins. This is known as the origin of the 

 lymph sacs by budding. 



Thus the study involves three elements : The nature of the lym- 

 phatic capillary, the nature of the lymphatic ducts, and the nature of 

 the first lymphatics or the lymph sacs. Bach one of these three lines of 

 proof involves the study of endothelium ; the first lymphatics are buds 

 from the endothelial lining of the veins ; these endothelial buds invade 

 the body down to the ultimate capillaries by the cell division of their 

 endothelial wall. 



A. GROWTH OF LYMPHATIC CAPILLARIES BY SPROUTING. 



A study of the method of growth of lymphatic capillaries is neces- 

 sarily associated with the study of the method of growth of blood 

 capillaries, for as far back as the time of Schwann (139), who first 

 saw the capillaries in the living tadpole's tail and who vaguely dis- 

 tinguished those which carried blood from those which had no cor- 

 puscles, there is a clear recognition that the two forms of capillaries 

 grow by the same method. This method Schwann thbught to be by 

 the addition of hollow connective tissue cells. 



The term growth by sprouting was introduced quite recently by His, 

 but the first description of the process dates back to the year 184-1. to 



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