REACTION OF LYMPHATIC ENDOTHELIUM 443 



injection, while others came out of blood vessels at some distance 

 away, moved past these leucocytes and finally reached the fat. 

 Such a leucocj^te which did not react to the presence of the fat 

 is illustrated as G in figure 8. It remained in practically the 

 same position throughout the observations, although it was 

 much nearer the injection site than several other leucocytes, 

 such as }^ upon which the fat exerted an attraction. An inves- 

 tigation of this question would be of interest in view of the dis- 

 covery of Fiessinger and Marie (10) that lymphocytes contain 

 Hpase, while polymorphonuclear leucocytes contain the protein 

 splitting enzyme. 



The present studies were completed in the spring of 1916, 

 before the work of Wislock" (28) had been published, and were 

 made without the aid of trypan blue. In the study published 

 in 1909 (3), the results of staining tad-poles with neutral red 

 was described, and neutral red was used in the present experi- 

 ments, also. This stain is not specific in its reaction since it 

 stains the epithelium intensely and all tissues rather faintly. 

 Nevertheless, on focussing beneath the epithelium upon the 

 field of observation for the experiments, it was noticeable that 

 the red granules of the stain were confined almost wholly to 

 two types of cells, namely, to the endothelial cells of the lym- 

 phatic capillaries and to the pigmented leucocytes. A very few 

 red granules were scattered along some of the blood capillaries, 

 but in the lymphatic endothelium, the stain was quite dense and 

 had collected in clumps which were located chiefly in the peri- 

 nuclear areas. Pigmented leucocytes, which had taken up the 

 stain, were scattered at various points through the fins, and their 

 presence was much more conspicuous, on account of their num- 

 bers and the intensity of their staining, in the region where the 

 fatty substance had been injected. It would be interesting to 

 determine whether or not these leucocytes, which show a special 

 affinity for the injected fat, would also stain with trypan blue — • 

 to discover whether or not they too should be classed as 'pyr- 

 rhol cells.' 



