LYMPH-FLOW AND LYMPHATICS, CHICK EMBRYOS 427 



(1) The muscular movements of the embryo 



(2) The pulsations of the lymph heart 



(3) The condition of the blood circulation 



(4) The development of valves 



(5) The development of new lymphatics in various regions 



1) The muscular movements of the embryo. As previously 

 stated, these embryonic movements occur periodically, about 

 once a minute. While one of these violent spasms is taking 

 place, injected ink granules which had previously been moving 

 along a channel in a definite direction are brought to a stand- 

 still and then forced back and forth within the vessel and they 

 do not resume their interrupted journey until after the cessation 

 of the movements. This temporary alteration of the lymph- 

 flow, produced by the embryonic movements, was noticed in all 

 the stages studied. The movements of the embryo also exert 

 an important indirect influence on the lymph-flow at certain 

 stages of the early circulation owing to their intimate connection 

 with the first pulsations of the lymph heart. In chicks of 6^ to 

 8 days, the lymph heart beats occur only during the periods of 

 body movement. Hence paralysis of the movements in such 

 embryos alters the lymphatic circulation greatly. This will be 

 referred to in the discussion of the next factor. 



2) The pulsations of the lymph heart. The experiments 

 demonstrated clearly that the commencement of lymph heart 

 pulsations is the factor which instigates the lymphatic circulation 

 in the posterior part of the body. In the earliest stage of pul- 

 sation, the lymph-flow almost ceases in the interval of rest 

 between the group of lymph heart beats which accompany each 

 muscular spasm, and the plexus of vessels composing the lymph 

 heart fills up with blood. If chloretone (1 : 4000 in warm Ringer's 

 solution) is dropped on the embryo, the lymph heart beats are 

 paralyzed along with the muscular movements and in this case 

 the lymph heart plexus and the adjacent superficial lymphatics 

 become filled with blood, while the circulation in the anterior 

 lymphatics continues undisturbed. 



As the pulsations of the lymph heart become stronger, the 

 area of superficial lymphatics draining into it becomes increasingly 



