92 BACTERIOLCGY. 



in liot saturated solution of f uchsine in aniline water, washed in water, 

 dried on filter paper, and mounted in balsam. The tannin solution 

 consists of 1 part of tannin to 100 cc. of 50 per cent, alcohol. 



Nicolle and Morax also, have modified Lofiier's method. Per- 

 fectly clean cover-glasses are used, and the film is dried without 

 fixing in the flame. Cover-glasses are covered with the mordant, 

 and heated for about ten seconds, and when steam rises the mordant 

 is shaken off and the film rinsed with water. The same process is 

 repeated three or four times, and finally the cover-glass is stained 

 with Neelsen's solution, holding it over the flame once or twice 

 for a quarter of a minute ; it is then washed and examined. 



Bunge prefers as a mordant a mixture of aqueous solution of 

 tannin with 1 in 20 aqvieous solution of sesquichloride of iron in the 

 proportion of 3 parts of the tannin solution, 1 part of the iron 

 solution, with the addition of 1 cc. of a saturated watery solution of 

 f uchsine added to 10 cc. of the mixture. The mordant is kept before 

 use, and applied for five minutes. The preparation is then washed and 

 stained with Neelsen's solution. In another plan the cover-glasses 

 are immersed for one half to one minute in 5 per cent, solution of 

 acetic acid, washed and dried. The mordant is then applied three or 

 four times, and the cover-glasses washed, dried, and then stained with 

 gentian-violet, dipped in 1 per cent, acetic acid, washed, dried, and 

 mounted. Peroxide of hydrogen may be added to the mordant, 

 drop by drop ; it becomes reddish-brown in colour, and must be 

 shaken up and filtered before use. Cover-glasses are exposed to its 

 action for about a minute, and Neelsen's solution is used for 

 staining. 



Hessert dispenses with the mordant. The film is fixed by 

 treating cover-glasses with a saturated alcoholic solution of corrosive 

 sublimate. After washing, the cover-glass is stained for thirty to 

 forty minutes in a hot dye, by preference a 10 per cent, water j' 

 solution of saturated alcoholic solution of f uchsine. 



Cover-glass Impressions. 



One of the most instructive 'methods for examining micro- 

 organisms is to make an impression-preparatimi. This enables us, 

 in many cases, to study the relative position of individual micro- 

 organisms one to another in their growth on solid cultivating media, 

 and in some cases produces the most exquisite preparations for the 

 microscope. A perfectly clean, usually small-sized, cover-glass is 

 carefully deposited on a plate-cultivation, and gently and evenly 

 pressed down. One edge is then carefully levered up, with a needle, 



