OF THE LYMPHATIC SYSTEM OF THE CHICK. 469 



embryos. When the posterior lymph-heart fails to develop, the lymph-flow in the 

 pelvic lymphatics does not start in chicks of 6 to 7 days and, coincidentally, definite 

 lymph-channels do not appear in this region. On the other hand, in the anterior 

 part of the superficial lymphatic plexus the circulation begins and the earliest ducts 

 are formed in a normal manner. 



OPERATION 2. REMOVAL, OF ANTERIOR POINT OF ORIGIN FOR THE SUPERFICIAL LYMPHATICS. 



As already stated, a plexus of lymphatics, situated beneath the shoulder and 

 connecting with the veins in the region of the duct of Cuvier, was injected in chicks 

 of 5 to 7 days. Connections from this plexus with the superficial side plexus through 

 the axilla can always be injected in embryos of 5 days and older. This plexus, on 

 account of its situation and relation to the venous system, has been thought to be 

 homologous with the jugular lymph-sac of mammals (Sabin) and has been con- 

 sidered to be the point of origin for the lymphatics of the anterior part of the body, 

 including those of the side region. 



In starting experiments to remove this region of origin we first attempted to 

 destroy the jugular (anterior cardinal) vein before the development of any lym- 

 phatics. This proved to be a rather difficult procedure and various methods were 

 tried out and abandoned the electric cautery and radium, because of the difficulty 

 of localizing the burn; suturing of the vein with minute shreds of cloth, because of 

 excessive injury to the delicate tissues, etc. We finally succeeded in removing the 

 vein by the following method: Boiled and filtered aqueous Berlin blue was injected 

 into the jugular vein in the head region. This material clumps on contact with the 

 blood and sticks to the vessel wall, thereby plugging the vessel and at the same time 

 rendering the wall visible. The injection was stopped at the proper moment so as 

 to prevent the entrance of the blue granules into the heart. By this means the 

 jugular vein, the duct of Cuvier, and a plexus of capillaries in the region of the 

 posterior cardinal vein were injected and their circulation stopped. All of these 

 injected vessels were then dissected away with sharp needles, and some of the tissue 

 around them, as far anteriorly as the ear vesicle, was also removed. 



This operation was performed on chicks of 42 to 48 hours. On examination 

 4 to 6 days later it was found that in every case a well-developed jugular vein was 

 present on the operated side. In one case this was larger than the corresponding 

 vein on the unoperated side. In other chicks it was somewhat smaller, but in all 

 of them it was unquestionably present. It would seem that we were justified in 

 concluding that conditions are present in the neck region which favor development 

 of a large vein. This result, although of interest in connection with the problem of 

 the development of blood-vessels, did not carry us any farther in the solution of the 

 problems connected with the lymphatic system. In all of these specimens a normal 

 plexus of lymphatics could be injected in the region of the thoraco-epigastric vein, 

 which connected in a normal manner with a deep lymph-plexus, which, in turn, 

 connected with the newly-regenerated jugular vein. 



We next tried to isolate the side region, between the wing and leg, from the 

 region beneath the shoulder, from which its lymphatics were supposed to be derived. 



