106 



Finally make permanent stained mounts of these threads 

 by transferring a small portion of this drop culture to a 

 minute drop of water on a clean cover-glass ; spread, dry, 

 fix and stain the preparation in the usual manner. 



Stained preparations. Place about two dozen clean 

 cover-glasses on the lid of a slide box. Pick up a piece of 

 the spleen, kidney or liver in a pair of forceps, and while 

 holding the cover-glass down with another pair of forceps, 

 lightly streak the cut surface of the organ over the cover- 

 glass. A very thin and even film is desirable. In this 

 way streak all the cover-glasses, then allow them to dry 

 in the air and fix cautiously by passing once or twice 

 through the flame. These cover- glasses are commonly 

 known as streak preparations. 



Stain some of the fixed cover-glasses will) simple ani- 

 lin dyes, as gentian violet or i'uchsine ; examine and 

 study the specimens carefully and make permanent prep- 

 arations. The remainder of the cover-glasses will serve 

 for double-staining by Gram's method. 



Gramas method. This excellent method for demon- 

 strating the presence of certain bacterin, as anthrax, in the 

 fluids and tissues of the body is based upon the fact that 

 the protoplasm of the bacterial cell when stained with 

 anilin water-gentian violet, and then treated with iodine 

 forms a difficultly soluble compound. By proper exposure 

 to a solvent the dye can now be removed from the entire 

 cover-glass, but not from the bacterial cell. The deeply 

 stained violet rods lie on a colorless back-ground, which 

 on treatment with a contrast color, as eosine or picro car- 

 mine, becomes stained a light pink. The method is as 

 follows : 



A solution of anilin water-gentian violet is first pre- 

 pared. Anilin oil is placed in a test-tube to a depth of 

 about half an inch. The tube is then filled with water, 

 closed with the thumb and thoroughly shaken in order to 

 obtain a saturated aqueous solution of anilin. The liquid 

 is then passed through a small filter and collected in 



