102 



HARDWICKE'S SCIENCE-GOSSIP. 



remarks treat of mounting in general, and the beginner 

 applies to insects methods suitable to histological, 

 vegetable, or mineral objects. His principles are at 

 fault, and his productions are more or less failures. 

 This paper is not about mounting in general, and, 

 although many of the methods detailed may be good 

 for other classes of objects, it is only for the prepara- 

 tion of insects and similar things that they are here 

 recommended. 



In preparing any object, one's aim should be to 

 obtain an absolutely correct idea of it. One should 

 therefore endeavour firstly to set it up in a natural 

 manner and position, and secondly to display every 

 detail. It is always to be borne in mind that details 

 shown by distortion give an incorrect idea of the 

 object, and that the knowledge thus gained being in- 

 accurate, is therefore nearly useless. 



By the ordinary method of preparing insects, every- 

 thing is sacrificed to the display of minute details, 

 and preparers are ambitious of doing on one slide 

 what can only be properly done on two, three, or 

 four. This ambition results in a radical fault, namely 

 the use of undue pressure, in order to bring all parts 

 of the object to one level. Again, a wish to mount 

 slides rapidly induces the employment of heat in order 

 to harden the balsam quickly. For mounting diatoms, 

 a skilful manipulator tells me that hardening the 

 balsam thus brings out the markings. His slides 

 fully bear out his words. But for insects, nothing 

 can be worse than heat, for it produces an opalescent 

 transparency, which makes markings partially invisible, 

 and this effect is aided by the increased density given 

 to the balsam. 



The methods which I venture to recommend avoid 

 the use of undue pressure and of heat, while, at the 

 same time, not only will they give a better general 

 idea of an object than the methods ordinarily in use, 

 but also will bring out details much more distinctly. 



Insects cannot all be mounted in the same way, 

 and, according to the points which it is desired to 

 show, so must the method of mounting vary. I will 

 first describe the various media and processes of 

 mounting, and then say something of the different 

 insects for which they are suited. 



The media I employ may be divided into two 

 classes : A, those which are aqueous, and B, those 

 which are resinous. 



Class A. Medium i. — To every fluid ounce of 

 glycerine add ten drops of ordinary acetic acid. 

 Almost everything may be mounted in this medium. 

 Medium 2. — Glycerine jelly. For details of its manu- 

 facture I refer readers to Science-Gossip 1874, P- 54- 

 Carbolic acid should be used to prevent the growth 

 of fungi, instead of Baric chloride as there stated. 

 I do not recommend glycerine jelly, except in a 

 very few instances, and therefore I do not trouble 

 the reader with what I said at a former time. 

 Medium 3. — Distilled water. To every fluid ounce 

 of water add 20 drops of carbolic acid ; boil until 



the acid be dissolved, and filter through blotting- 

 paper. This medium is solely for mounting specimens 

 of opaque objects. 



Class B. Medium 1 . — Canada balsam. I consider 

 test-tubes by far the most convenient vessels in which 

 to keep this resin. Fill a test-tube with two-thirds of 

 old balsam and one-third of benzine. A friend tells me 

 that new balsam does just as well, but of that I have 

 no experience. The mixture should be of the con- 

 sistency of cream. Medium 2. — Gum dammar. Take 

 two parts of gum dammar and one part of gum mastic : 

 pound them in a mortar, and fill a test-tube quite full 

 of the powder, but do not ram it down : now pour in 

 benzine until the test-tube will hold no more. Cork 

 the tube tightly, and let it stand in an oven for a few 

 hours, until the solution be quite clear and all 

 sediment has sunk to the bottom. Filtering is quite 

 unnecessary. Gum dammar by itself dries very brittle, 

 and besides, I have never been able to clarify it. 

 These mixtures of Canada balsam and of gum dammar 

 may be used indifferently for unstained specimens. 

 I do not know that one is better than the other, but 

 for stained specimens it is better to use only gum 

 dammar, because the natural oils in the balsam cause 

 some colours to fade. 



Process i. To mount an object in glycerine. — A 

 cell is necessary for all but the very thinnest objects. 

 Fixing a cell is some trouble, but it is seldom that 

 anything deeper is required than a glass slip with a 

 countersunk cell. As some people are always com- 

 plaining (quite needlessly) of the difficulty of "seal- 

 ing cells," I describe my method : fill the cell with 

 glycerine ; pick out all air bubbles with a pair of 

 forceps, put the object in the cell ; take up the thin 

 glass cover with the forceps, breathe on its underside, 

 and place it carefully (do not drop it) on the cell ; 

 press the cover down, taking care to keep the object 

 in the middle, and secure it with a clip. Leave the 

 slide for an hour in order that all superfluous 

 glycerine may be pressed out ; then take it up and 

 wash it in clean water by dipping it in, and moving 

 it gently backwards and forwards. Wipe the ends of 

 the slide with a towel ; absorb all the water about 

 the cover with blotting-paper, and then varnish it 

 very thinly with ' Bell's cement.' Knotting varnish, 

 such as is sold in ordinary oil shops will answer the 

 purpose, but slides sealed with this are apt to leak. 

 Therefore I prefer Bell's cement, which can be bought 

 at C. Baker's, High Holborn. Three coats of varnish 

 should be put on before the clip is taken off, and the 

 slide may then be " ringed " on the turn-table in any 

 way that suits the mounter's fancy. 



For mounting in jelly I again refer readers to the 

 back number of Science-Gossip. Objects may be 

 mounted in water in the same way as in glycerine ; 

 washing the slide after putting on the clip, however, 

 is unnecessary. 



Process II. To mount in balsam or dammar. — 

 With a turn-table draw a ring of water-colour paint 



