MICROSCOPICAL EXAMINATION OF BACTERIA. 91 



held over the flame until steam rises. The mordant is then washed 

 off with distilled water, and all traces removed from the edge of 

 the cover-glass with alcohol. The stain is filtered, and a few drops 

 allowed to fall on the film, and after a few minutes the cover-glass 

 is again very carefully warmed until steam rises. The stain is then 

 washed off with distilled water, and is ready to be examined and 

 subsequently mounted. For some bacteria it is necessary to modify 

 the solutions, either by the addition of acetic or sulphuric acid, or 

 by varying the quantity of soda solution. 



Trenkmann introduced a modification of Lbffler's system. Cover- 

 glasses are floated for from two to twelve hours on a solution 

 consisting of 1 per cent, tannin and g per cent, hydrochloric acid. 

 After washing in water the preparation is stained with a saturated 

 alcoholic solution of any of the aniline dyes diluted in the propor- 

 tion of- 2 drops of the dye to 20 of water. The cover-glasses 

 which remain in the solution for from two to four hours are then 

 washed in water, and examined. The best results are obtained with 

 carbolised fuchsine, diluted in the proportion of 2 drops to 20 drops 

 of 1 per cent, carbolic. Trenkmann also recommended the use of 

 catechu and logwood as mordants, with the addition of very dilute 

 acid, and subsequent staining with fuchsine. 



Lutesch suggested the use of ferric acetate. To avoid any 

 deposit on the surface of the preparation, freshly prepared saturated 

 ferric acetate is used, and 5 to 10 drops of acetic acid are added to 

 16 cc. of the mordant. After warming the solution the preparation 

 is washed in water, followed by 20 per cent, acetic acid, again 

 thoroughly washed, and then stained with hot sokition of fuchsine or 

 gentian-violet in aniline water. 



Van Ermengem. used a mordant composed of 1 part of 

 2 per cent, solution of osmic acid, 2 parts of 10 to 25 per cent, 

 solution of tannin, with to every 100 cc. of this mixture 4 or 5 drops 

 of acetic acid. A black ink is thus formed, and the solution is 

 applied for from five to thirty minutes. After washing in water and 

 alcohol the cover-glasses are placed in a sokttion of nitrate of silver 

 and transferred to another solution composed of 5 grammes of gallic 

 acid, 3 grammes of tannin, 10 grammes of acetate of soda, and 330 

 grammes of distilled water. In a few moments they are again placed 

 in nitrate of silver, and then washed and mounted in balsam. 



Sclavo's method answers well for certain micro-organisms. The 

 preparations are left for one minute in, solution of tannin, washed in 

 distilled water, transferred for a minute to 50 per cent, phospho- 

 molybdic acid, again washed and stained from three to five minutes 



