L8 /.'. Sabin. 



Thus there can be [uestion in regard to the method of growth 



of the peripheral capillaries. Bi th blood and lymphatic capillaries 

 iv the activity of the protoplasm of their walls. The endo- 

 thelium at the growing tip ia a syncytium, the processes advance and 

 ede; they are tiny, hair-like vessels, and they receive tlicir nuclei 

 'ii the parent stem. There are differences in the appearance of the 

 two t\ capillaries probably associated with the pn and 



nee of the circulating blood and the difference of function. The 

 lymphatics have very many more tiny sprouts, only a few of which 

 are permanent; that is, their wall is much more amoeboid and the 

 much more irregular. Thus on positive evidence, oamely, the 

 of the process ui the Living Eorm, whjch is the best evi- 

 dence known to anatomical science, we are justified in the conclusion 

 that capillaries grow by sprouting. 



I'.. \.\ VI'll \ I lo \\|. \ii\-U M I'll A I 1. ZOK 



second argument in Eavor of the venous origin and the centrif- 

 ugal growth of Lymphatics by their own endothelium is that it 



3hown that lymphatic vessels gradually invade the body from certain 

 limited -. Thus if injections of vessels are made from th 



in larger and larger embryos an evi asing /"tie of 



lymphatic capillaries can be demonstrated. Moreover, for each stage 

 the zone of vessels is constant. 



I iegan my work with the study of the development of lymphatic 



nds in the embryo pig and to obtain injections of them introduced. 

 oeedle into the foot pads. By taking younger embryos a sta 

 was soon readied when no injections of the foot pad- ever entered 

 lymphatics, but al I one could still injed - in the 



skin over the body. This was the beginning of the proof that lym- 

 phatics bud oil' from the vein- and grow peripheralward instead of the 

 3abin l'."- 1 ). 



In an embryo pig 5 cm. long (Sabin L30, fig. 5) a simple p 

 lymphatic capillaries has al st i atirely covered the body. I say capil- 

 laries advisedly, adopting Ranvier's (US, p. 74) criterion of val 

 for lye ducts in contrasl to then- absence in I 

 The body i- first invaded by lymphatic capillaries, and the primary 

 plexus shown in fig. :. (Sabin L30), which is the anlage of the d< 

 subcutaneous plexus, was injected by a single puncture of the nee, lie. 



