VITAL STAINING OF CORNEAL EPITHELIUM 39 



original epithelial surface or may be absent here and there, do not 

 usually exhibit neutral red granules and show no activity. 



2. The next layer (fig. I, &), which is the uppermost layer in 

 some preparations, consists of cells which contain in the cyto- 

 plasm the most minute red granules, almost uniform in size. 

 These appear in abundance after prolonged intense staining. 

 The contour of the individual cells is hardly visible at first. 

 In som_e instances, especially when the rapid method of staining 

 was employed, larger granules appeared in the cells so abun- 

 dantly that they almost filled the cell body, leaving only a clear 

 round or oval space in the center, occupied by the nucleus. 



3. The basal cells (fig. 1, a), which are evidently smaller than 

 those of the upper layers, exhibit, as a rule, distinct and much 

 larger granules, not very uniform in size, and often more numer- 

 ous on one side of the nucleus than on the other. 



4. Between the two latter layers frequently another layer of 

 cells (fig. 1, b) is visible. These are intermediate in size between 

 the cells of the basal layer and those of the layer above, and as 

 regards the arrangement of the colored granules show a resem- 

 blance to the cells of the second layer. 



Furthermore, between the second and third layers there were 

 found a number of deeply red stained bodies, round or irregular 

 in shape, some of which showed a more deeply stained red spot 

 (one of these is shown in fig. 1, a, and another in fig. 2, a). The 

 origin of these bodies is unknown. 



When the culture is observed several hours or more after the 

 preparation, the cells of the upper and basal layers are easily 

 distinguishable according to the distribution of granules in their 

 cytoplasm, and this becomes more marked as the tissue becomes 

 more translucent. The individual granules were sometimes 

 observed to coalesce gradually, changing in shape. 



When the tissue is intensely stained, the cells of the connective 

 tissue and of the posterior endothelium also show distinct gran- 

 ules which are usually not so abundant and are more or less dis- 

 tinguishable from those of the epithelimn. The nucleus re- 

 mains unstained throughout. 



