74 Florence R. Sabin. 



lymphatic system can be seen and drawn. This was done by Clark. 

 The specimen was then cut in serial sections and both blood capillaries 

 and lymphatics were reconstructed. Two reconstructions were made, 

 one with the 4 mm. Zeiss objective, and the other with a 2 mm. Zeiss 

 oil immersion lens. Both reconstructions show that neither blood 

 capillaries nor lymphatic capillaries can be reconstructed completely. 

 More is obtained with an oil immersion lens, but both powers show 

 capillaries in the form of rows of beads (figs. 5, 6 and 7, Clark 26, 

 copied as figs. 513 and 514, Sabin 134). 



This test of Clark's is the best possible test, because it is a recon- 

 struction of exactly the same specimen from which the original draw- 

 ing was made. This point cannot be made in testing the method of in- 

 jection and that of reconstruction. For this test I ( 135 ) used, however, 

 symmetrical plexuses in the same embryo. An embryo pig 27 mm. 

 was chosen in which there was an almost complete injection of the occip- 

 ital superficial lymphatics. Many of the sprouts on the margin had been 

 ruptured. The injected plexus could of course be reconstructed, while a 

 reconstruction of the empty lymphatics on the opposite side showed the 

 entire plexus split up into isolated vessels (figs. 6, 7 and 8, Sabin 135). 

 On the injected side there was just one lymphatic vessel which did not 

 receive the injection mass, and there was an extravasation just at its 

 base. This is readily explained by the fact that vessels are often con- 

 nected by very slender strands to the main plexus, as, for example, the 

 vessel near the point of injection in fig. 18, and a rupture might readily 

 occur in such an area before the end of the vessel was reached. 



The test of the two methods has now been made a third time by 

 Mrs. E. E. Clark (27) in her injection of the jugular lymphatic 

 plexus in a stage corresponding to the one which Miller (97) has 

 reconstructed. The two results are shown in figs. 14 and 15. 



A comparison of the injected jugular sac in a pig 18 mm., shown in 

 fig. 7, with reconstructions of the corresponding stages in the eat 

 (figs. 60 to 62, Huntington 55), also brings out the same point that, 

 wherever the injection method can be applied, it demonstrates more 

 continuous lymphatics in an area than can be reconstructed, even as 

 isolated vessels. 



Undoubtedly an occasional blood capillary or lymphatic capillary 

 may separate from the main plexus and atrophy, but the apparently 

 isolated vessels found in serial sections along the course of grow- 

 ing lymphatics connect in life. Lymphatics do not grow by de- 



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