1891.] MICROSCOPICAL JOURNAL. 63 



directed, as violent and dangerous explosions might result. The pro- 

 cess as given above is perfectly safe and very effective." 



If the student does not choose the mode of separation prescribed by 

 Monro, he may, by using a long dipping tube, arrive at somewhat the 

 same results. The washed and clean deposit may be stirred up in a 

 cylindrical glass measure, and the drippings of the first sediment ex- 

 amined under the microscope. He will then probably find large grains 

 of sand mixed with the lai"ge specimens of diatoms. Dr. Carpenter 

 recommends that these diatoms should be pushed on one side by means 

 of a bristle inserted in a wooden handle. If this plan is adopted great 

 gentleness must be used, as even with such a comparatively delicate 

 instrument a rough touch will end in the fracture of the fragile frustule. 

 For this purpose Prof. Redfern suggested the use of split hairs, such as 

 may often be found in an old shaving brush. These do not appear to 

 split until they are pressed on the diatom, when they open and grip it 

 like fairy forceps ; but even here care must be employed lest a fracture 

 of the valve ensues. Mr. William Borrer, Jr., devised an arrangement 

 for picking out and arranging diatoms which was attended with great 

 success. It may be described as a collar of cork fitted on the lower end 

 of a low-power objective, and through which a needle is thrust 

 obliquely. To the end of the needle one of the barbed lancets of a 

 bee's sting, or what is even better, the bristle from a rat's tail, is ce- 

 mented. By adjusting the point of this in such a manner as to be in 

 focus at nearly the same time as the diatom, it can be brought down on 

 to it gently, and, as it adheres to the barb, it can be raised and trans- 

 ferred to a clean slide. Some mounters of diatoms acquire dexterity in 

 cleaning, selecting, and mounting these minute frustules, as evidenced 

 by the slides of A. C. Cole and L. Hardman, and the still more marvel- 

 lous achievements of Herr Moller. The student will generally be con- 

 tent if he can mount diatoms cleanly and suitably for his own satisfac- 

 tion. 



Of late years a search has been made with the \ie\v of finding a suit- 

 able medium in which to mount diatoms. Balsam stands a chance of 

 being relegated to the back row, the fault found with it being its low 

 index of refraction when used with the high-power immersion lenses, 

 but taken all round, and except for comparative tests, it is far the most 

 convenient medium. Gum styrax finds support from some, and a prep- 

 aration introduced by Dr. Van Heurck, of Antwerp, of which styrax 

 forms a good proportion, gives very good results, and at the same time 

 is convenient. Its mode of use is simple. A small portion is warmed 

 slightly and put on a warm cover-glass, which is inverted, and gently 

 allowed to fall on the side on which the diatoms are placed. Not too 

 much heat must be employed or annoying air bubbles will form, and 

 not too much pressure used or the diatoms will be broken. This prepa- 

 ration is very dark to look at in the mass, but as a very thin layer ex- 

 ists between the cover and the slide it may be regarded as sufficiently 

 colorless for this and for man}' other mounting purposes. It remains 

 unchanged in character for j^ears. American styrax hardens just like 

 balsam, but when heated becomes extremely fluid. Having a high i"e- 

 fractive index, it is particularly useful for the finer diatoms. On ac- 

 count of its fluidity when heated it is better for the smaller diatoms 

 during the process of mounting lest the cover sink down on the larger 

 forms and crush them. 



