MICROSCOPIC OBJECTS. 



25 



siable. They can easily be manufactured 

 at home by anyone who has a little skill, 

 by cutting rings from glass tubing with a 

 sharp flat file. Various cements may be 

 used for attaching the cell to the glass 

 slip ; marine glue is the most trustworthy, 

 but is somewhat difficult to manage, as it re- 

 quires a strong heat to melt it. Gold-size, 

 when good, is equally reliable, but the vari- 

 ous cements which have been used of late 

 years for mending broken china and glass, 

 such as coaguline, appear to be quite satis- 

 factory, and being colorless, look best when 

 used with glass cells. 



2. Moitnting in Balsam. — Whole insects 

 are usually prepared and mounted in the 

 following way: Having killed the insect, 

 either by means of the cyanide bottle, or by 

 immersion in spirits, it is set out carefully 

 between two glass slides, which are tied to- 

 gether and put in a strong solution of pot- 

 ash — caustic potash one ounce, water twen- 

 ty ounces. Here it must remain for some 

 time, according to its color and texture; 

 but a frequent examination of the speci- 

 men is necessary, as some insects dissolve into 

 a jelly if kept in potash too long. One or 

 two days will suffice for most specimens, 

 but others will take longer. When it be- 

 comes sufficiently soft, it is taken out of 

 the potash, placed in a saucer of pure wa- 

 ter, and gently pressed with a soft brush 

 until the contents of the thorax and abdo- 

 men are expelled. It must then be washed 

 with fresh water until quite clean, when it 

 must again be set out on a slide in the po- 

 sition which it is finally to occupy, covered 

 with a square of thin glass, and tied down 

 with thread. Here the treatment may 

 vary. The older method was to keep the 

 slide in a warm place, under cover, until 

 the preparation became quite dry, and then 

 immerse it in turpentine. 



The objection to this plan was that the 

 insect became full of air, which it is almost 

 impossible to expel, unless by the aid of an 

 air-pump. The better method is, to drain 

 all the water from the insect after washing, 

 using blotting paper if necessary, and then 

 immerse it in alcohol and water for about a 

 day, and after that in pure methylated spirit 



to displace all the water. A second dose 

 of pure spirit may be necessary in some 

 cases. The whole of the water will thus 

 be removed by the spirit, which will also 

 render the preparation so firm that, on the 

 application of the balsam, it will not alter 

 from the position in which it was set. 

 When quite free from moisture a few days' 

 soaking in turpentine will give most speci- 

 mens the necessary transparency. Some in- 

 sects and parts of insects may, however, 

 require to be left in turpentine for several 

 weeks before they are fit to mount. 



The tissues of some dark-colored insects 

 are best treated with some bleaching agent 

 immediately after their removal from the 

 potash solution: one of the best is as 

 follows : 



Hydrochloric acid, . 10 or 12 drops. 

 Chlorate of potash, ... | dram. 

 Water j ounce. 



This will remove the objectionable strong 

 browns and yellows of the chitinous por- 

 tions, which are so fatal to obtaining a 

 good photograph. By examining the object 

 occasionally, the right amount of transpar- 

 ency will be gained, but it is best not to 

 let preparations remain too long in the 

 bleaching solution, because if too transpar- 

 ent they will be as difficult to photograph 

 as if too opaque. The writer recently pho- 

 tographed two splendid fly's tongues, or 

 ligulas, specially prepared by Topping. 

 These were selected out of seventy-two sim- 

 ilar preparations, but while both were per- 

 fection as microscopic objects, or for exhi- 

 bition in the lantern microscope, only one 

 was fit for photography. The other had 

 been bleached too much, and was too thin 

 to give a satisfactory photograph. 



When the necessary transparency has been 

 attained, and after the object has been suc- 

 cessively treated with alcohol and turpen- 

 tine, it is ready for mounting. A solution 

 of balsam in benzole is better than pure 

 balsam in many ways. The solution may 

 be prepared by "baking" pure balsam in 

 a slow oven until it becomes quite hard on 

 cooling, aud then dissolving in benzole, or 

 may be purchased at the shop of any opti- 



