HISTOLOGY OF THE THYMUS 305 



granules (fig. 2), and this was confirmed by a study of the hving 

 cells by means of vital stains. 



While the protoplasm of the reticular cells has a fine fibrillary 

 structure, it was not possible to demonstrate fila to which the 

 granulae bore a definite arrangement. An alignment of the 

 granules in rows was not found in the reticular cells, in the sec- 

 tions. In the myoid cells, however, the granulae or rods are 

 arranged in definite rows at regular intervals upon a fibrillar 

 groundwork, and to this is due the apparent cross-striation of 

 the fibrillae and their resemblance to muscle fibers. 



While the granules and filaments of the myoid cells are readily 

 demonstrable by all the mitochondrial stains, they appear with 

 equal distinctness after formalin fixation and prolonged staining 

 with Heidenhain's iron hematoxylin after mordanting in 4 per 

 cent alum. They are thus chemically distinct from the granulae 

 of the reticular and small thymic cells which cannot be brought 

 to view by this simple method. 



In sections stained according to the Meves-Deusberg modifi- 

 cation of the Benda method, the granulae are less numerous but 

 more distinct. They occur in groups in certain of the reticular 

 cells, and are quite variable in size, the largest being about half 

 as large as the nucleus of a small cell; the largest granules or 

 droplets may show partial decolorization. They are almost 

 always spherical, but occasionally are slightly elongated and 

 somewhat irregular (figs. 3 and 4). 



There remain to be noted certain cells with coarse slightly 

 rod-shaped or bacillus-like granules, which stain intensely with 

 crystal violet, even after fixation in Zenker-formol. These cells 

 are scattered irregularly through cortex and medulla. They' 

 are not numerous but by reason of their deep staining and the 

 large size of their granules, are very conspicuous. These cells 

 are probably identical with the gentianophilic cells described by 

 Prenant (8). Their identity with the eosinophile cells is ques- 

 tionable, although Prenant suggests this possibility, and states 

 that the eosinophiles of the blood are also gentianophilic. The 

 elongated character of the granules would, however, serve to 

 differentiate these cells from the eosinophiles in which the gran- 

 ules are spherical. 



