Appendix B: Some Standard Reagents and Their Uses 183 



g) Impregnation of Epithelia, etc. Place the fresh tissue, 

 preferably a ihin membrane, into a 4 per cent, solution of meth- 

 ylen blue in normal saline. To demonstrate the outline of cells, 

 leave the tissue in the stain not longer than 10 minutes. To get 

 a negative image of lymph spaces, canals, etc., in contrast to the 

 ground substance which becomes deeply impregnated, leave the 

 tissue in the stain 20 to 30 minutes. For this purpose it is 

 advisable to remove any membranous covering which invests the 

 organ. In either case, after staining, fix the tissue for 30 to 40 

 minutes in a saturated aqueous solution of ammonium picrate, 

 changing it once or twice, and examine in dilute glycerin. To 

 preserve the preparation permanently, proceed as in 6). To do 

 away with the macerating action of the ammonium picrate, add 2 

 per cent, of a 1 per cent, osmic-acid solution to the fixing bath. 



56. Methyl Green. This is one of the best of the nuclear 

 anilin stains. It is particularly valuable because it instantly 

 stains the chromatin of nuclei in fresh tissues. Use in strong 

 aqueous solutions, acidulated to about 1 per cent, with acetic acid. 

 It does not give a satisfactory chromatin stain if the tissue has 

 been fixed in acetic acid or mixtures containing it. It follows 

 pure corrosive sublimate solution admirably. 



57. Methyl Violet. This stain is commonly used in 0.5 to 2 

 per cent, aqueous solutions for staining bacteria, nuclei, and amy- 

 loid. It may often be substituted for gentian violet. 



58. Neutral Red. Neutral red is used widely as an intra vitam 

 stain. It is a good stain for cytoplasmic granules, and in some 

 cases for mucus cells. For intra vitam staining it may be used in 

 the same way as methylen blue (with the omission of fixation). 

 For staining fixed material, a 1 per cent, or stronger aqueous 

 solution is employed. Granules are stained orange red (bright 

 red in acid medium, yellow in alkaline medium). Rosin finds 

 that in nerve cells stained in neutral red (followed by water, acid- 

 free alcohols, xylol, and balsam) nucleoli and Nissl's granules 

 are stained red, the rest of the cell yellow. 



59. Orange G. This is an excellent cytoplasmic stain and is 

 often used on sections as a contrast to carmine, hematoxylin, and 

 safranin. Grtibler's Orange G is the most reliable. It should be 



