80 Florence B. Sabin. 



state with great certainty on the basis of many injections that the 

 jugular sac has a complete endothelial wall and is a closed vessel. 

 It is thus clear that Kampmeier has not demonstrated that this upper 

 part of the thoracic duct replaces degenerating veins. 



The chief point, however, in Kampmeier's work is not that some 

 of the lymphatics replace degenerating veins, but that they develop 

 out of tissue spaces. As the chief proof of this theory he uses a 

 reconstruction of an injected specimen of mine. Notwithstanding the 

 fact that this injection is the only one which has yet been made in a 

 mammal in this early stage, Kampmeier does not hesitate to call it 

 complete. It was injected indirectly through the jugular lymph sac, 

 from which the injection mass ran into the thoracic duct. At a cer- 

 tain point in the injection there is an extravasation (Kampmeier, 

 fig. 13, line 15), and in exactly the same position in the next section 

 is a large endothelial-lined empty space. It is therefore merely an 

 arbitrary decision whether the empty vessel was actually connected 

 with the injected part or not, that is to say, there is as much evidence 

 for the one view as for the other. No one who has had experience with 

 the injection method would be sure that the first injection in a new 

 region was a complete one. The spaces which Kampmeier has shown 

 as lymphatics in my specimen are lined by endothelium; that is, 

 they are the spaces with which Lewis (76) has made us familiar; 

 they are not the mesenchyme spaces which Kampmeier and Strom- 

 sen regard as the anlage of lymphatics. 



Stromsen (146a) has injected the prsevertebral lymphatics in turtles 

 and finds that in advance of the injected zone there are enlarged 

 tissue spaces which he thinks are going to become lymphatics. Kamp- 

 meier says that it is easy to select tissue spaces which are going to 

 become lymphatics for, " histologically, all incipient lymphatic an- 

 lagen, whether they are spaces independent in position or spaces fol- 

 lowing, transforming and expanding the discarded pathways of 

 redundant venous channels, are decidedly different from either an 

 active vein or a mature lymphatic " (Kampmeier 66a, p. 430) . Strom- 

 sen (146, p. 354) adds to this ability to select tissue spaces which are 

 going to become lymphatics this further point, that such enlarged tis- 

 sue space occur only in the pathway of developing lymphatics. These 

 two points can be easily disproved by anyone who has access to serial 

 sections of embryos. For example, why were not the enlarged tissue 

 spaces in Kampmeier fig. 3 selected as lymphatics? Good examples 



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