1890.] MICROSCOPICAL JOURNAL. 253 



and stable mounting medium, so that in the event of the object under 

 examination proving of interest, it will only be necessary to let the 

 fluid be dried up around the edge of the cover-glass when it mav be 

 cemented with gold size or stifl' gum dammar varnish. 



Another useful fluid mountant will be found in a nearly saturated so- 

 lution of acetate of potash. It is found valuable in the mountin^^ of 

 vegetable preparations. The preparation being placed on the glass 

 slide under the cover, the solution may be added drop by drop till the 

 intervening space is filled, when it may be sealed with cement. Its re- 

 fractive powers arc not equal to glycerine, but in cases where glycerine 

 is not admissible, this will lie found an excellent substitute. 



Preservative fluids vary according to the substance to be mounted, 

 whether it be vegetable or animal, whether the animal be marine or 

 fresh water, and even different parts of the animal body require their 

 suitable medium. 



Whatever mounting medium be employed, nothing conduces more 

 to success than neatness in manipulation and regularity in arrangement. 

 And mounted specimens add considerably to the pleasure of keeping a 

 cabinet if all the slides are correctly labelled, and no specimen should 

 be put aside without a temporary label. If the student intends return- 

 ing to it for further observation, it is hopeless to say it will be remem- 

 bered. A month or two after, a doubt will arise in the mind, and six 

 months after, its source, name, its very nature, are involved in obscur- 

 ity. It will then be thrown away, for its usefulness as an instructive 

 agent has vanished. A simple plan when preparing a series of slides 

 is to have some of the gummed bordering of postage stamps rolled on 

 a reel and hung up near the mounting table. When a slide is prepared 

 and before placing it in the cabinet, put on a temporary label from this 

 roll, write with pencil the name of the object, and any particulars rel- 

 ative to the mounting medium, etc. Not only should the slides be la- 

 belled, but it adds considerably to their neat appearance if the mounts 

 are in the centre of the slide. It is sometimes not an easy matter, es- 

 pecially with delicate or fragile objects, to get them into this desired 

 position, but, by gentle coaxing, or by a judicious floating on to the slide, 

 if a thin section, it may be made to occupy the centre. There are, how- 

 ever, some substances whose constitution is sufliiciently robust to stand 

 a good deal of pushing about. A small piece of apparatus has been 

 used by the writer for some years with satisfaction, and maybe adopted 

 with great advantage. Thereby the object may be centred with great 

 facility. A thin plate of wood covered with white paper, and rather 

 larger than an ordinary standard slide, should have a wooden ledge glued 

 along one side, and shorter ones at the ends, thus enclosing an area 

 which will receive tightly the glass slide on which the object is to be 

 mounted. If two lines are drawn diagonally across this space from the 

 opposite corners, their intersection will be the exact centre of the slide. 

 Taking this intersection as the centre, circles corresponding to the size 

 of the circular cover-glasses usually emploved, may be struck with a 

 compass, and in this way objects mounted within the circles seen 

 through the glass slide must be centrallv placed. It is desirable some- 

 times to be able to examine an object from both sides. It may be thus 

 accomplished — procure two thin strips of wood of the standard size, 

 from the centre of one cut out a square three-quarters of an inch sitlc, 

 from the other cut out a square seven-eighths ot an inch side, glue the 



