216 Another Hint on Selecting and Mounting Diatoms. 



siderable use to amateur microscopists. In last April's number of 

 the same Journal appeared a friendly notice of it in a letter from 

 Capt. Knight, in which, acknowledging the advantage of making 

 classified collections of diatoms, he speaks of the difficulty of pro- 

 curing the material for so doing, and observes that professional 

 mounters and opticians will only sell you their mixed gatherings, 

 set, as a general rule, in balsam ; though occasionaUy, but seldom, 

 a dry mount may be obtained, when it is an easy matter to remove 

 the cover and select the requhed forms. He does not, however, 

 appear to think it possible to utilize for the purpose the balsam- 

 mounted material, and I suspect others as well as myself have till 

 now been of the same opinion. My friend Mr. Tatem has, however, 

 turned his attention to the subject, and has discovered a very easy 

 plan for picking out any desired forms from such slides for the 

 purpose of remounting them. He has kindly communicated his 

 method to me, and permitted me to publish it as an addendum to 

 my former paper. Having both of us given it a fair trial we can 

 confidently recommend the plan, which is as follows :— 



Place the balsam-mounted slide on the hot plate, and when it is 

 sufficiently warmed tip over the cover by means of a needle ; the 

 diatoms will be either on it or the slide, it matters not which. 

 Apply over them at once, whilst still on the hot plate, a drop of 

 turpentine, remove the slide to the stage of the dissecting micro- 

 scope, and add more turpentine. Have ready a clean shp of glass 

 on which has been placed a drop of turpentine. In the case of 

 large discoid and other forms, having applied plenty of turpentine, 

 they can be easily transferred by means of a fine sable-hair brush 

 from the original slide to the pool of turpentine on the clean one. 

 In the case of finer forms it is better to place less turpentine on the 

 original slide, collect the diatoms into a heap, allow the turpentine 

 to dry a Httle, and then by a twist of the brush to transfer them 

 en masse to the new slide. In either case, having got them there 

 push them together and mop up the superfluous turpentine, and 

 then, still under the dissecting microscope, slant the slide by placing 

 a piece of folded paper under one end, and apply a little benzole 

 either by means of a clean brush or glass rod immediately above 

 them, that is, on the end of the slide that is raised, and allow it to 

 float gradually over them, care being taken that it does not flow 

 with too great a rush and carry away the diatoms with it. Kepeat 

 this process some half-dozen times, till the whole of the turpentine 

 and balsam has been washed away, and till the valves are left dry 

 and black after the benzole is evajjorated. They can then be trans- 

 ferred in the usual way to any other slide, and even with greater 

 ease than from an ordinary dry gathering. I may as well add that 

 if gum has been used to fix the diatoms, it may be found that some 

 of the valves, especially the discoid ones, remain obstinately adherent 



