Floreuee K. Sabin 189 



this level is the line between the subcntaneous tissue and the chorium. 

 When the needle enters the subcutaneous tissue in pigs from 3 to 8 cm. 

 long the injection mass spreads out in straight lines and forces a path 

 for itself in the tissue spaces. When the needle enters the chorium the 

 injection mass raises a bleb on the surface. In neither of these cases, 

 that is, when the injection mass has entered the tissue spaces of the 

 subcutaneous tissue or of the chorium in small embryos, have I ever suc- 

 ceeded in getting a lymphatic injection. To obtain a perfect injection 

 without any extravasation at the point of puncture one must enter the 

 needle at exactly the right level, that is, between the subcutaneous tissue 

 and chorium and then inject slowly. One then sees the ducts starting 

 out from the open slit in the injection needle. By giving a scarcely 

 perceptible pressure on the piston of the hypodermic syringe it is pos- 

 sible to inject the entire side of the embryo and have the individual 

 ducts leading from the needle stand out clearly at the end, that is, to have 

 no extravasation. Thus it will be noted that it is necessary to puncture 

 the ducts in order to get a lymphatic injection. 



In Fig. 5 the ducts have covered the body and only the feet, a part of 

 the head and the tail remain unsupplied. It will be noted that the' 

 ducts from the different centers in the neck have anastomosed so freely 

 in the skin that it is not easy to see just where the primary points of 

 radiation lie. Moreover, the ducts for the anterior part of the body 

 have anastomosed so freely over the surface of the body with those for 

 the posterior part that it is possible to inject into the ducts over the 

 ilium and have the injection mass pass toward the veins in two ways; 

 first through the ducts that come to the surface over the crest of the 

 ilium, and secondly by an indirect course through the channels over the 

 side of the body to the ducts in the neck. 



In a pig 6.5 cm. long the spreading of the superficial lymphatics in 

 the skin is practically completed. That is to say, ducts have been in- 

 jected to the top of the head, the snout, the ears, eyelids and toes. In 

 these areas, far from the centers of growth, the plexus of ducts is not 

 abundant at this stage, indeed, to use one area as an example, only a 

 few of the advance sprouts over the top of the head have actually anas- 

 tomosed with the ducts of the other side. However, no area of the skin 

 is wholly without lymphatics. In other words, the invasion of the skin 

 by lymphatics is complete though the plexus of lymphatics in the skin 

 is very incomplete. 



To sum up : In the anterior part of the body there are three main 

 centers from which the superficial ducts spread out; first, in the pos- 

 terior part of the neck, for the ducts over tlie back of the head and over 



