GRA A/'S ME THOD OF S TA I MING. 3 5 



time required for the section to become stained varies also with the 

 temperature, and the above periods may be considerably shortened if 

 the temperature be slightly raised. When sufficiently deeply stained, 

 the sections are washed in distilled water, then in weak acetic acid, 

 and again in distilled water. If the colour is to be allowed to remain 

 in the nuclei, the section should be mounted at once in Canada 

 balsam, dammar varnish, Farrant's solution, glycerine jelly (prepared 

 by dissolving one part of gelatine in six parts of water, adding seven 

 parts of glycerine and one per cent, of carbolic acid ; heating the 

 whole, and then filtering whilst warm), a saturated solution of acetate 

 of potash ; or for Bismarck brown preparations, glycerine. 



Where alcohol and clove oil are used in the process of mounting, 

 great care should be taken that the sections are not allowed to remain 

 too long in either of these fluids, or by their continued solvent action 

 even the dyes in the bacteria may be partially or wholly removed, 

 if not at first, after the lapse of some time. If the nuclei are to 

 remain unstained, and the sections are to be cleared up as much 

 as possible, the section is stained, afterwards washed in distilled 

 water, and then transferred to a five per cent, solution of carbonate 

 of potash, by which the colouring matter is discharged from all the 

 tissues except the bacilli or micrococci. This method is invaluable 

 for the demonstration and enumeration of bacilli contained within 

 vessels or thick sections, as in intestinal mycosis, where the anthrax 

 bacilli are to be observed in situ in the capillary vessels of the in- 

 testinal villi. 



In place of a watery solution, a saturated alcoholic solution of 

 almost any of the germ-tinting aniline colours may be made up in 

 large quantity, and diluted as required with about ten times its bulk 

 of distilled water or of aniline oil water. — (Weigert.) 



Gram's Method of Staining. 



25. Perhaps one of the most satisfactory methods is that recom- 

 mended by Gram. All specimens to be stained by this method should 

 be preserved in absolute alcohol, and should be transferred at once to 

 Weigert's or Ehrlich's gentian violet, or fuchsin and aniline water solu- 

 tion (§ 27, p. 40), where they may remain for from one to three 



