Florence E. Sabin 357 



Material and methods. — The material for the present study has been 

 embryo pigs of all stages. In studying the development of the nodes, 

 just as in studying the development of the ducts, it is essential to employ 

 injections, both lymphatic and arterial, and these injections have been 

 made in every stage. The lymphatics have been injected by means of a 

 hypodermic syringe, with either saturated aqueous Prussian blue or 

 with India ink. The material has been preserved for the most part by 

 the injection of a saturated solution of bichloride of mercury, either into 

 the aorta or into the umbilical vein. The blood-vessels are usually first 

 washed out with warm salt solution, then the bichloride introduced and 

 continued until the embryo is hard and white. The injection is made 

 slowly with a pressure of about 100 mm. of mercury and the bichloride 

 allowed to stay in the vessels from one-half to two hours. It is then 

 washed out thoroughly by injecting 70 per cent alcohol through the same 

 canula. The embryo is then placed in 80 per cent alcohol over night and 

 the next day transferred to 95 per cent alcohol. This method involves 

 the least possible shrinkage, indeed it may be made to produce a slight 

 distension of the tissues, which is an especial aid in studying lymphatic 

 nodes.^ 



In studying the developing nodes in fresh tissue, it is readily noticed 

 that they ^are sometimes found distended with fluid and sometimes col- 

 lapsed. It is just as easy to tell with the unaided eye when a node is 

 thus distended with lymph as to distinguish between the mesenteric 

 lymph nodes distended with chyle or collapsed and empty. This method 

 of injection produces the same distension of the spaces that occurs nor- 

 mally when the node is in active function; that is to say, it makes the 

 lymphatic ducts rounded rather than collapsed. This explains the espe- 

 cial value of the method as applied to lymphatic tissue. 



A valuable aid in the localization of the nodes, and especially in 

 studying the relations of the lymph hearts to the developing nodes, is 

 found bv making injected embryos transparent.' The lymphatics are 

 first injected with India ink and then the entire embryo is placed in 

 95 per cent alcohol. They are left in the alcohol until they are shrivelled. 

 This takes at least two weeks. The embryos are then cleared in a dilute 

 solution of potash from 1 to 2 per cent, taking from 1 to 4 hours. The 

 specimens are preserved in glycerine, at first 20 per cent and later in 

 pure glycerine. 



^ McFarland : Jour, of App. Microscopy, Vol. II, No. 10, and Myers, Ibid., 

 Vol. VI, No. 12, and J. H. Bull., 1905. 



■* Mall: American Journal of Anatomy, Vol. IV, 1905, p. 6. 



