ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 707 



solution of caustic potash. Without any further preparation the 

 bacteria may then be recognized under a power of 400-500, particu- 

 larly if a light pressure is applied to the cover-glass so as to disengage 

 the bacteria more completely from the detritus which surrounds them. 

 To distinguish them more clearly from the other bacteria, the cover- 

 glass may be dried by passing it rapidly two or three times through a 

 flame and then staining by a concentrated aqueous solution of aniline 

 violet or other colour. The bacteria of tuberculosis are absolutely 

 colourless, while the other bacteria, micrococci, &c, are plainly 

 coloured. The whole process only takes ten minutes. 



Preparing' Diatoms.* — Dr. E. S. Warren gives detailed directions 

 for the preparation of diatoms, especially for separating them from 

 sand and broken species, the directions for which hitherto published 

 he thinks are insufficient. Coarse sand may be got rid of by repeated 

 settlings and decantations, but it is different with the fine sand. 

 Graduated settlings and decantations have been advised, but these are 

 insufficient, as despite all care, more or less of light silt will float 

 with the light forms of diatoms, and the heavy forms will fall to 

 the bottom with the heavy sand. Whirling in an evaporating dish 

 has been advised, but this is insufficient, and Dr. Warren has found 

 no method better than the one he has used for several years, and 

 which he has never seen described or hinted at except in regard to 

 whirling."]" 



" If the material contains the lighter forms only, I first use 

 whirling force as follows : — I take an evaporating dish of a size 

 according to the quantity of material, and fasten it on the wheel of 

 my turntable by means of a narrow rubber band passed over it and 

 under the wheel. The material is diffused in five or six times its 

 bulk of water. An empty wide-mouth bottle is near the turntable, 

 and should have the capacity of two or three times the quantity of 

 diffused material. Shaking the material well, I fill the evaporating 

 dish about two-thirds, and then whirl it with considerable rapidity 

 till I think the sand has mostly settled at the bottom of the dish, 

 for the whirling motion causes it to fall. I then pour off the un- 

 settled portion into the empty bottle, and add more of the material 

 to the sand and diatoms remaining in the dish, and stir with a narrow 

 strip of glass; the whirling is repeated; and so on with all the 

 material. When this has been done, water is added to the portion in 

 tbe dish, and the process continued till no diatoms remain in the 

 sand. To ascertain this, the dipping-tube again comes into use. The 

 material is treated in this way several times, till no sand can be 

 obtained by it. If the material contains heavy diatoms like the 

 large Pinnularice, Triceratium favus, aud heavy disk-forms, the whirl- 

 ing process cannot well be used, for these heavy forms fall to the 

 bottom of the dish with the sand. 



" After the above process is ended, I proceed as follows, and this is, 



* Amer. Mon. Micr. Journ., iii. (1882) pp. 111-5. 



t Mr. F. Kitton subsequently (op. cit. p. 153) refers to his own papers in 

 ' Seieuce-Gossip,' 1877, pp. 115 and 217, as containing all or nearly all Dr. 

 Warren's methods. 



