186 Animal Micrology 



solution are left in the stains for from 24 to 48 hours. Decolorize 

 as directed under 29. 



66. Safranin and Gentian Violet. This is a combination that 

 is almost indispensable in the study of cell problems, especially 

 spermatogenesis. For formulae of stains see 44 and 65. Tissues 

 are best fixed in Flemming's or Hermann's solutions. Stain thin 

 sections for 36 to 48 hours in the saf ranin ; differentiate in alco- 

 hol very slightly acidulated (see 29), then stain for 5 to 10 min- 

 utes in the gentian solution and transfer the sections to Gram's 

 solution (see under 44) for 1 to 3 hours. Finally differentiate in 

 absolute alcohol. As soon as purple clouds have ceased to come 

 from the sections in absolute alcohol, they should be transferred 

 to clove oil for a few minutes and thence to xylol. The clove oil 

 seems to intensify the safranin in the chromatic granules, but too 

 prolonged an immersion in clove oil extracts the gentian violet. 



67. Silver Nitrate. The nitrate-of -silver method is used largely 

 as an impregnation method for work on nerve tissue and for dem- 

 onstrating intercellular substances and outlining boundaries of 

 cells in the epithelial coverings of membranes, etc. Wash the 

 fresh tissue in distilled water, then place it for 2 to 5 minutes in 

 0.5 to 1 per cent, aqueous solution of silver nitrate. Rinse in 

 distilled water, then expose the tissue to bright sunlight in water 

 or glycerin (or in 70 per cent, alcohol, if it be mounted in balsam) 

 until a brown coloration appears. Temporary mounts should be 

 made in glycerin. For application to nerve see chap. ix. 



68. Sudan III. This is a specific stain for fat. A saturated 

 alcoholic solution is used (5 to 10 minutes). Wash rapidly in 

 alcohol. Since alcohol is a solvent of fat, too long an immersion 

 will destroy the preparation. Mount in glycerin. With this dye 

 large fat drops stain orange, small ones yellow. The tissue should 

 have been fixed previously in Mtlllers fluid (8) or other medium 

 which does not dissolve fat. 



Van Giesen's Stain. See 43. 



69. Wright's Stain (for blood and for the malarial parasite). 

 See chap, xiv, memoranda 5 and 6. 



