Florence R. Sabin 373 



lymphatics. From this time on my attention was turned to the devel- 

 opment of the ducts rather than of the glands, because I was passing 

 to stages before the lymph glands were formed. 



At this time, following the suggestion of Budge's theory of the 

 thoracic duct developing from spaces behind the aorta, a needle was 

 introduced into the side of the neck of a very young embryo, and 

 passed behind the heart. The injection obtained proved to be venous, 

 but by taking larger embryos lymph ducts began to radiate out from 

 the point of injection; for example, in a pig 18 mm. long a few ducts 

 could be injected just at the point of puncture. For this injection the 

 needle was introduced straight inward at a point midway between the 

 ear and the upper border of the arm. At this stage, while it was 

 always possible to inject the small tuft of ducts at the neck, it was 

 never possible to inject ducts in any other part of the skin. Taking 

 a stage a little larger, a wider area or zone of lymphatics could be 

 injected from the same point in the neck, but none were injected in 

 any other place in the skin until the pig was 3 cm. long, when the 

 ducts could be injected just at a point over the crest of the ileum. 

 Taking a stage still larger a wider injection could be made from both 

 of these two points in the skin, one at the neck and one over the crest 

 of the ileum. The zone that could be injected at each stage was both 

 definite and constant and an increase of the pressure simply ruptured 

 the ducts at their tips instead of injecting them farther. Moreover, 

 at any point within a zone, ducts could always be injected subcu- 

 taneously in fresh specimens, while at all points beyond these zones 

 they could never be injected. 



Thus two points had been discovered as the result of many injec- 

 tions, from which the superficial lymphatics spread or radiated out to 

 cover the skin of the body and head. At a little later stage two other 

 points were found from which the ducts grew to the legs, one of these 

 being in the front of the neck, the other being in the inguinal region. 

 A large number of injections were made at. the two primary points until 

 a very complete series of the zones possible to inject at each stage was 

 obtained. This series included the stages from the time when the 

 ducts can just be injected at the side of the neck in a pig 18 mm. long, 

 up to the time when the ducts from the two points of radiation have 

 met and anastomosed over the side of the body of a pig 5.5 cm. long. 



The early stages of this development have been embodied in a dia- 

 gram or composite picture, Fig. 1. The picture includes pigs of four 

 different lengths, 1.8 cm., 3 cm., 3 cm., and 4 cm. Later stages are 



omitted to avoid confusion. The injections for the diagram were all 

 26 



