Journal of Applied Microscopy. 



159 



bacilli may be expected in the various 

 colonies that develop on the potatoes. 

 Some will be long, others short; some 

 will be narrow, others very thick; some 

 will grow in long threads, others in 

 pairs; some will have motion, others not. 

 At other times, the organism under ex- 

 amination will be perfectly round or 

 spherical, and in that case it is known as 

 a micrococcus. Again, the large oval 

 yeast cells may be met with. 



The examination of the living organ- 

 ism on an ordinary glass slide, in the 

 manner indicated, is not always satis- 

 factory, because the liquid soon begins to 

 evaporate and as a result rapid currents 

 are established in the liquid. To over- 

 come this evaporation it is customary to 

 examine the material in a hanging drop. 

 For this purpose a thick glass slide hav- 

 ing a concave well in the middle is made 

 use of. 



Fig. 2. 



The "hanging drop" is easily made in 

 the following manner: Place a small 

 drop of water on a clean cover-glass on 

 the table. The drop must be small 

 enough so that it will not run if the 

 cover-glass is placed on edge. The 

 growth from the potato is then touched 

 off into the drop of water by means of a 

 sterile platinum wire. A ring of vaseline 

 is then placed around the edge of the 

 well on the upper side of the concave 

 slide, by means of a bru.3h or match 

 stick. The slide, with its ring of vase- 

 line, is then inverted over the cover- 

 glass and gently pressed down. The 

 cover-glass now adheres to the slide, 

 which is then inverted. Care should be 

 taken to see that the vaseline is con- 

 tinuous around the edge of the well. If 

 such is the case, no evaporation of the 

 drop of water can take place and hence 

 the hanging drop can be examined at 

 leisure and without the presence of an- 

 noying currents in the liquid. Fig. 2 in- 

 dicates the hanging drop in longitudinal 

 cross-section. 



STAINING OF BACTERIA. 



One of the most important conditions 

 in order to obtain good results in stain- 

 ing bacteria is to have perfectly clean 

 cover-glasses. The latter should be so 

 clean that, when a drop of water is 

 placed on any of them and spread over 

 the surface by means of a platinum wire, 

 it will remain spread out as a thin film. 

 If it gathers in minute droplets, which 

 follow the wire and refuse to spread out, 

 the cover-glass is not clean and is not 

 suitable in that condition for staining 

 purposes. The thin layer of fatty matter 



must be removed, and this is often im- 

 possible to do if the ordinary procedure 

 is followed. The author's method of ob- 

 taining absolutely clean cover-glasses is 

 as follows: 



The cover-glasses are iir.mersed in 

 strong or absolute alcohol and then 

 wiped clean and dry with a clean piece 

 of muslin. They are then placed in an 

 Esmarch dish and heated in a dry-heat 

 sterilizer at a temperature of 180° to 200° 

 for one-half to one hour. The organic 

 matter remaining on the cover-glasses 

 is thus subjected to dry distillation and 

 is completely removed. The cover- 

 glasses thus treated will allow the 

 drop of water to spread over the en- 

 tire surface and when it dries it does 

 so evenly. 



Another procedure can be followed by 

 the beginner, if necessary, and that is to 

 pass the cover-glass six or eight times 

 through a Bunsen flame. This takes, of 

 course, more time and not infrequently 

 the cover-glass will crack. 



Anilin dyes are employed for staining 

 bacteria and it will be well to procure 

 two of these, fuchsin and gentian violet. 

 The crystals are added to strong alcohol 

 in a bottle till saturation results. The 

 two strong alcoholic solutions thus pre- 

 pared are never used as such, but are 

 first diluted. Inasmuch as the diluted 

 dye does not keep well, no more of this 

 should be prepared than is neces- 

 sary for several weeks work. Some of 

 the strong alcoholic solution of the dye 

 is placed in a one-ounce tincture bottle 

 and then diluted with three or four parts 

 of water. The bottle should be provided 

 with a cork through which passes a glass 

 tube, the lower end of which is slightly 

 drawn out. This then serves as a pipette 

 (see Fig. 3). 



Fig. 3. 



The cover-glasses and the dyes being 

 in readiness, the beginner can now pro- 

 ceed to stain the various bacteria found 



