VITAL STAINING OF CORNEAL EPITHELIUM 41 



therefore, does not seem to be a very favorable dye for the cor- 

 neal epithelium. 



Neither is 'methylene blue (rectif.)' suitable for the purpose, 

 as it fades too easily. 



So far as our observations go, 'gentian violet' did not give a 

 satisfactory result. Even the weakest solution, which stained 

 the cells, caused their death. 



'Brilliant cresyl blue 2 b' and 'methyl green' did not stain the 

 granules clearly, nor did 'indigo carmin,' 'toluidine blue,' or 

 'Utmus' give positive results. 



2. Staining of the cornea by administration of dyes in the 

 cmijunctival sac 



Arnold ('00) demonstrated neutral red and methylene blue 

 granules in the frog cornea by conjunctival administration of the 

 dyes in the fonn of fine powder. In this way typical granules 

 appeared in the cells, often causing injury. No experiments of 

 this kind are recorded in the presefit paper. 



3. Staining of excised, cornea 



In some experiments the cornea was first excised from the 

 animal and then stained. The tissue, after removal, was im- 

 mersed in physiological sahne solution containing neutral red, 

 freshly prepared, so that the epithelium became intensely red, 

 and could later be cultivated after thorough washing. The tech- 

 nique is simple and is useful in some particular instances. Usu- 

 ally, however, crystals appeared in the culture, when this method 

 was employed. 



4. Staining by addition of dyes to the culture medium 



Both neutral red and Nile blue, freshly dissolved in salt solu- 

 tion, were experimented with. They are easily soluble in pure 

 water, but not so easily if the water contains any salt (NaCl). 

 The appearance of crystals and the uneveness of the staining 

 proved this method to be an unsatisfactory one. Staining of 

 nucleus and granules by the use of gentian violet failed. Methyl- 

 ene blue stained granules, but it could not be employed for the 

 purpose on hand. 



