8 JOURNAL OF THE [January, 



The latter has also the great advantage of speed, as the mordant- 

 ing is effected in less than a minute. 



Both Loefider, and Nicolle and Morax, have advised the repeti- 

 tion of application of the mordant two or three times in some 

 cases. In this I have found no apparent gain ; the entire action 

 of the hot mordant on these minute bodies seems to be completed 

 during a single brief immersion. 



In all these methods much loss of time would be incurred from 

 treating the covers, as advised, one by one, with drops of mor- 

 dant and of colorant over a flame. I have elsevvhere' already 

 indicated the far easier, quicker, and more convenient staining 

 carried on in a wire spring holding a dozen or more covers, 

 with film downward, in the hot mordant or hot stain in a small 

 flask. The dried coloring and overstaining may be thus obvi- 

 ated, for which Loefiler prescribes washing in absolute alcohol. 



We may now consider the application of these methods to 

 various micro-organisms, availing ourselves of useful suggestions 

 from the writers referred to. 



Preparatmis of Bacteria. — In making mounts from pure cul- 

 tures the following process is now used in our laboratory. After 

 drying of the film it ordinarily requires only ten to fifteen min- 

 utes for the staining and complete mounting of the preparation. 

 In three or four drops of sterilized water, in a flamed watchglass, 

 stir very gently a particle or droplet of the pure bacteria culture 

 (taken preferably from the surface of a growth on potato or 

 agar) on a platinum wire loop or use until a slight cloudiness is 

 produced ; then take it all up at once within a sterilized drop- 

 tube with rubber bulb. Lay a series of thoroughly cleaned thin 

 covers (treated in Seiler's solution and washed in distilled water 

 and pure alcohol) on the bottom of a shallow two-inch Petri dish. 

 Apply to each, and spread very gently, a drop of the diluted 

 culture, and immediately add to the centre of the drop a drop- 

 let of the selected fixative (say, tannic acid or chromic acid solu- 

 tion). If a sparser distribution of the bacteria is desired, allow 

 the drop to settle a few minutes, take up and incline each cover, 

 and remove excess from lower edge. Allow to dry, with pro- 

 tection from dust, at the natural temperature of the room, or 



' "Suggestions In Microsc-ipical Technique," this Journal, ix. C1893). 26. 



