EXAMINATION OF BACTERIA WITH THE MICROSCOPE. 55 



Dissolve the hematoxylin in the alcohol, and the am- 

 monia alum in the water. Mix the two solutions. Let 

 the mixture stand four or five days uncovered; it should 

 have become a deep purple. Filter and add the glycerin 

 and the methyl alcohol. After it has become dark enough, 

 filter again. Keep it a month or longer before using; the 

 solution improves with age. At the time of using, filter 

 and dilute with water as desired. 



LITHIUM-CARMINE (ORTH). 



Carmine 2.5 grams. 



Saturated watery solution of lithium carbonate. loo.oc.c. 



Add a few crystals of thymol. The carmine dissolves 

 readily in the lithium carbonate solution. Filter the stain 

 at the time of using. Sections are to be left in the stain 

 five to twenty minutes. 



Sections stained in carmine are placed directly in acid 

 alcohol (i part hydrochloric acid, 100 parts 70 per cent. 

 alcohol) for five to ten minutes. They acquire a brilliant 

 scarlet color. When used as a contrast-stain for tissues 

 containing bacteria, it is best to use it before staining the 

 bacteria, which might be decolorized by the acid alcohol. 



Staining of Blood-Films. The method of Wright is 

 the one recommended. It is applicable to bacteria and to the 

 parasite of malaria, and is useful as a general stain for 

 blood. Films of blood are prepared as directed in chapter 

 VII., Part I., and are allowed to dry. 



(a) The stain is poured over the surface of the prepara- 

 tion till it covers it. This serves to fix the film of blood. It 

 is allowed to remain for one minute. 



(6) Add distilled water, drop by drop, till a reddish tint 

 appears at the edges and a metallic scum forms on the sur- 

 face. About six drops are needed for a three-fourths inch 

 cover-glass. The real staining of the preparation now takes 

 place, and requires two or three minutes. 



