452 



SCIENCE 



[N. S. Vol. XXXIX. No. 1004 



sions of the dye by the cells of Kupfer of 

 the hepatic capillaries and in the kidney 

 to a similar behavior shown by the epithe- 

 lial cells of the proximal convoluted tubules. 

 The spleen and lymph glands are stained a 

 paler though still brilliant blue and the 

 color is due in these organs to the granules 

 carried by the so-called reticular and by the 

 true lymphatic endothelial cells. 



In the testis the interstitial cells of Ley- 

 dig are stained brilliantly, although the 

 granules here are singularly regular and 

 intermediate in size between those possessed 

 by cells of type one and two in the skin. 

 In addition, true vitally stained connective 

 tissue cells of type two are also present be- 

 tween the seminiferous ducts, but the epi- 

 thelial cells of the seminiferous tubules 

 never contain the slightest trace of the dye. 



The pancreas possesses in the connective 

 tissue septa of its acini brilliantly stained 

 cells of type one, although no particle of 

 the dye is found in the pancreatic paren- 

 chyma. 



The thoracic cavity presents a remark- 

 able picture, for its deep blue walls enclose 

 the lungs which have preserved their normal 

 pink color, and in which few vitally stained 

 cells are found. The heart, however, con- 

 tains many of these, for not only do the 

 epicardial cells receive the dye like the 

 mesothelial ones, but also many connective 

 tissue cells of type one infiltrate its mus- 

 culature at many points. 



The thymus, thj^roid and parathyroids 

 owe their generally lighter stain to similar 

 cells which follow the connective tissue in 

 its structural relation to these organs. 



Most remarkable is the behavior of the 

 central nervous system, for with the excep- 

 tion of the hypophysis and choroid plexus 

 the nervous system contains no trace what- 

 ever of the dye, and its whiteness in con- 

 trast to the stain of the other tissues is a 

 strange sight, the more so because the dura 

 is always densely stained. 



With the exception of the kidney, the 

 epithelium of whose convoluted tubules 

 comes from the middle germ layer, the 

 great mass of the epithelium of the body 

 refuses to react to the stain. Most remark- 

 able also is the rejection of the dye by the 

 blood cells, whose polymorphonuclear ele- 

 ments have always been supposed to play 

 so great a role in phagocytizing foreign 

 particles. 



It might possibly be supposed from the 

 comparative physical measurements we 

 have made on the dyes that the so-called 

 vital stains or vital granules, which we 

 have just described, are an expression 

 merely of diffusion, especially inasmuch as 

 the most diffusible dyes of this class are 

 the most satisfactory vital stains; but we 

 have explicitly pointed out that heightened 

 diffusion powers effect the vital stain merely 

 by enabling the dye molecules or dj^e-mol- 

 ecular-complexes to present themselves to 

 the class of cells which wUl receive them in 

 every corner of the body. Having arrived 

 at the cell, the dye by no means diffuses 

 into it, as we can see, for instance, various 

 basic dyes (neutral red, methylene blue, 

 janus green) diffuse into a cell, advancing 

 from periphery to center, and lodging 

 often with special avidity in some pre- 

 formed granule or structural element of the 

 cell (e. g., mast cell granules with thionin or 

 neutral red, Nissl bodies with methylene 

 blue). The benzidine dyes, let in more 

 slowly at the cell's periphery, never en- 

 counter physical conditions which favor 

 their rapid spread and they are disposed of 

 by the cell by being concentrated at va- 

 rious points where they are doubtless set 

 apart from the cell 's protoplasm. The vital 

 granules then deserve their designation, for 

 they are always the result of the behavior 

 toward the dye on the part of a living cell. 

 Dead cells behave quite differently, for into 

 their protoplasm, including the nucleus, 

 the benzidine dyes diffuse rapidly, produc- 



