52 Florence R. Sabin. 



for all the sacs in the human. They all become completely trans- 

 formed into a group of lymph nodes except the cisterna chyli, which 

 is partially though to a varying degree transformed. The lymph 

 sacs make the great primary groups of nodes for each region through 

 which lymph must pass before entering the veins. Thus for example 

 in the intestines the preaortic nodes are the primary group and they 

 come from the retroperitoneal sac, while the nodes of the mesentery 

 are secondary, tertiary, etc. Thus we may define primary lymph 

 nodes as those that are derived from the lymph sacs, and they are 

 also primary in the sense of being the first to develop for a given 

 region. It therefore seems to me that it is fair to conclude that 

 the lymph sacs of the mammals, which represent the lymph nodes, 

 take the place of the lymph hearts of the amphibia. They do not 

 of course represent the same function, for they never have any 

 muscle, so they never pulsate, and from the beginning they must 

 cause a slowing of the lymph flow rather than a hastening of it and 

 this slowing must become much more marked as they are transformed 

 into lymph nodes. Thus they seem to me analogous to amphibian 

 lymph hearts. 



From the preceding analysis of the literature, it is clear that 

 there is a general agreement among recent workers that the mamma- 

 lian lymph sacs precede the lymph vessels, and hence form a primary 

 lymphatic system and that these sacs are derived from the veins. 

 This position has been very greatly strengthened by the work of 

 Favaro^^ and Allen, ^'^ on the lymphatic system in fishes, and by 

 Knower^^ and Hoyer,^^ in the amphibia. 



Favaro discovered that in fishes the lymphatics come from the veins, 

 and that here the relation of the lymphatics to the veins is much 

 more primitive than in mammals. Lymph hearts and vein hearts 

 may be present, moreover one and the same vessel may carry either 

 blood or lymph either at the same time or at different times. Thus 



"Favaro. Atti R. 1st Veneto di sc. lett. ed arti, 1905-06, T, 65, Parte secouda. 

 Appendice alia Dispensa 10. Octobre 1906. S. 279. Venezia 1906. 

 "Allen. Proceedings of the Washington Academy of Sciences, Vol. IX. 1907. 

 '"Knower. Anat. Record, Vol. II, 1908. 

 '''Iloyer. Bulletin de I'Acad. d. Sciences d. Cracovie, 1908. 



