788 Transactions of the Society. 



The tubes, having received their occupants, should be kept in 

 a place where they can be easily examined. I find it a good 

 system to rig up a box into divisions by means of double cross 

 strings ; by this I can store about five dozen tubes of ordinary size 

 in a box 10 inches by 4 inches, and by means of the number on 

 the cork can abstract any particular tube at pleasure. The reason 

 for being able to obtain easy access to the specimens during their 

 preparation is this : in a short time the fluid -will become more or 

 less discoloured, the mature ova of Crustacea are especially liable to 

 cause this ; that of fishes gives off a milkiness which would be 

 simply ruinous to a slide, and plants would obviously stain the 

 fluid with chlorophyll. These various discolorations can however 

 be overcome by repeated washings. The tubes should be overhauled 

 occasionally and their contents washed as follows: pour off the 

 discoloured fluid gently, so as not to lose any of the objects, then 

 fill up the tube with distilled water ; the specimens, owing to their 

 being charged with a heavier fluid, sink rapidly, and thus allow 

 the tainted water to be poured ofi" ; repeat this operation until the 

 water carries off no more extraneous matter, and then pour in 

 some fresh fluid as before. It will be found necessary to allow 

 some specimens to remain in preparation, with periodical washings, 

 for six or eight months, but I have many that have been so treated 

 for two years, with the result that they are exceedingly clear and 

 beautiful. The majority of objects may however be finally 

 mounted in less time, although I do not consider that marine 

 objects would remain clear with less than at least three months of 

 such preparation. 



Having thus referred to the construction of the cell and the 

 preparation of the object, I will describe the final stage of mounting. 



A cell having been thoroughly cleaned, a rim of cement should 

 be applied to its upper edge, and upon its becoming nearly set, 

 which can readily be noticed by its losing its gloss and becoming 

 dull, the cell should be filled to a convexity with fluid. The fluid 

 I use for this part of the ojieration differs considerably in density 

 from that used in the preparation of the objects ; for instead of 

 3 parts alcohol, 2 parts glycerine, and 1 part distilled water, I use 

 a fluid as weak in some cases as 6 parts distilled water to 1 part 

 each of alcohol and glycerine. Here again, however, discretion 

 must be exercised, for such proportions are only safe to use when 

 the specimen to be mounted is thoroughly well preserved in the 

 stronger fluid first, and if such be not the case, a stronger mounting 

 medium than this must be made. 



Having then filled the cell with fluid, the object should be 

 placed in it and a few seconds allowed for the mingling of the two 

 fluids of different density, which will often set up rotatory motions 

 of a remarkable character amongst the objects. When this motion 



