LYMPH-FLOW AND LYMPHATICS, CHICK EMBRYOS 407 



b. The absence of valves in this early stage, and 



c. The fact that there is not enough fluid entering the lym- 

 phatic capillaries from without to force out the blood, or, in 

 other words, that the pressure in the veins is higher than that 

 in the lymphatics. 



As the presence of stagnant blood indicates, there is no cir- 

 culation in these earliest lymphatics. Granules introduced into 

 various parts of this primitive plexus do not move along within 

 the vessels, although the violent periodic movements of the em- 

 bryo force them back and forth within the lymphatics. 



Figure 1 represents the injected superficial lymphatics in a 

 chick of 5 days and 6 hours, and shows the character of the two 

 plexuses before they have united. 



OBSERVATIONS OF THE EARLY LYMPH-FLOW AND ASSOCIATED 



CHANGES IN THE FORM OF THE LYMPHATICS IN CHICKS OF 



DIFFERENT STAGES 



The various changes in the pattern of the superficial lym- 

 phatics are illustrated in figures 2 to 7, and the direction of the 

 lymph flow, as shown by the movement of granules in the living, 

 is indicated by arrows in the drawings. 



The lymph-flow, in the superficial lymphatics, commences in 

 chicks of approximately 5 days, 18 hours (measuring from 15 

 to 17 mm. before fixation). When a living chick of this age was 

 observed under the binocular microscope with brilliant illumi- 

 nation, lymphatics containing stagnant blood could be seen in the 

 form of a continuous plexus of irregular vessels which was 

 present in the tail region and over the pelvis. Anterior to the 

 leg the amount of blood was more scanty and the lymphatics 

 consequently more difficult to see, while along the anterior part 

 of the side and in the axillary region, only a few scattered knobs 

 of blood indicated the position of the blood-filled plexus visible 

 in chicks a few hours younger. 



WTien one of the lymph vessels situated on the pelvis, in such 

 an embryo, was punctured and a few granules of ink deposited 

 in its lumen, they remained at the point of injection. At the 

 time of the periodic muscular movements, the ink granules were 



