402 ELEANOR LINTON CLARK 



physiological and morphological changes which take place in 

 the developing lymphatic system, after its primary differentiation. 

 The problems of the origin of the Ijrmphatic endothelium, the 

 formation of new capillaries, and of the manner in which the 

 l>^nphatics reach the various organs of the bod}'' are not con- 

 sidered here. 



For the past three years at the Johns Hopkins University 

 and during the present 3^ear at the University of Missouri, Dr. 

 Clark and I have been engaged in a study of the development of 

 lymphatics in chick embryos. In 1912, we published prelimi- 

 nary reports' of a part of this work, in which we stated that the 

 early lymphatics are filled with stagnant blood and can therefore 

 be seen in living embrj'os and distinguished from the blood 

 capillaries. At the suggestion of Dr. Clark, I undertook to 

 study the process by which this blood clears out of the superficial 

 lymphatics, by injecting a few granules of India ink into the 

 blood-filled lymphatic plexus, in living chicks, and observing 

 their fate. It was soon found that this method afforded an 

 opportunity for testing the early flow of lymph, since granules 

 deposited in a vessel of the superficial plexus soon became dis- 

 lodged from the point of injection and moved along definite 

 paths, previously invisible. 



METHOD 



The method employed for keeping chicks alive for these experi- 

 ments was the same as that previously reported for our earlier 

 observations. A window was made in the egg-shell and the 

 shell membrane stripped off, after which the allantois was folded 

 back and the amnion opened and drawm aside, exposing the whole 

 side of the embryo to view. The egg was then placed on the 

 stage of a binocular microscope, which was enclosed in a warm 

 chamber, heated to incubator temperature. At frequent inter- 

 vals during the course of the observations, a small amount of 



^ E. L. Clark, General observations on early superficial lymphatics in living 

 chick embryos. Anat. Rec, vol. 6, no. 6, 1912. E. R. Clark and E. L. Clark, 

 Observations on the development of the earliest lymphatics in the region of the 

 posterior lymph heart in living chick embryos. Anat. Rec, vol. 6, no. 6, 1912. 



