04 



THE ART OF MAKING MICROSCOPE SLIDES 



Insect skeleton 



squirt in jets of alcohol to free the speci- 

 men. It does not matter if tlie specimen 

 should stick to one of the two shdes for 

 it may then be mounted on this slide. 

 Whether, however, the specimen is free in 

 alcohol or adherent to one shde, it must 

 now be cleared, and the use of turpentine 

 for this purpose is strongly recommended. 

 As soon as the specimen has cleared, it is 

 placed in the center of the shde and a 

 considerable quantity of natural balsam 

 poured on top of it. Since this specimen 

 will not be danaged by heat, it should now 

 be warmed until the balsam is hot and as 

 hquid as water. Tliis drives off the turpen- 

 tine, as well as most of the natural solvent 

 of the balsam, so that when the covershp 

 has been placed and the slide cooled it will 

 be finished. Excess balsam may then be 

 scraped and washed off in the usual man- 

 ner and the specimen labeled. 



The description just given is of the con- 

 ventional method of preparing mounts of 

 this type and may be equally well apphed 

 to parts as well as to entire insects. The 

 preparation of demonstration mounts with- 

 out "pressure is now a lost art, and there 

 appears to be no one alive to duplicate the 

 feats of the old mounters of the last cen- 

 tury who were able to turn an entire 

 housefly into what appeared to be an am- 

 ber glass model of itself. For the benefit, 

 however, of those who may wish to resur- 

 rect this art, the author would hke to 

 offer a few suggestions as to a method by 

 which he has prepared passable, but not 

 good, shdes of this type. The insect, re- 

 laxed exactly as if it were being prepared 

 for a museum specimen, is then " set" on a 

 glass slide, with the legs arranged in the 

 required position and held in place by 

 cementing the tip of each leg to the shde 

 with a small drop of molten gelatin. 



A piece of wood is whittled down until 

 it can be slid between the insect and the 

 glass, thus stopping the legs from con- 

 tracting and pulling the insect down in the 

 next stage of hardening. The glass with its 

 attached insect should then be placed in 

 95% alcohol and left for a week to harden. 



If, at this stage, it is placed directly in 

 alkah, the ligaments of the legs will be 

 softened and the specimen will no longer 

 be set in a natural position. It is, however, 

 possible, after the specimen has been re- 

 hj'dratod, to drill a very small hole in the 

 back of the ajjdomen and to work a hypo- 

 dermic needle forward until the tip of it 

 reaches to the head. A minute quantit}^ of 

 10% potassium hydroxide is then injected 

 and the specimen left in a moist chamber 

 for two or three hours. The needle is then 

 reinserted and a further quantity of po- 

 tassium hydroxide injected. By this time 

 some of the viscera will have been softened 

 sufficiently to come out of the hole on the 

 edge of the needle. Care must be taken 

 that none of the hydroxide gets onto the 

 legs, or onto any of the fine appendages, 

 and particularly that it does not run down 

 and dissolve the gelatin which is holding 

 the specimen in place. After three or four 

 days of making injections daily, the vis- 

 cera of the insect will have been washed 

 out and the body itself commencing to 

 soften. The slide is then put into alkali, 

 where it remains until the legs of the 

 specimen start to soften and to be trans- 

 parent. The specimen is then taken to 

 glacial acetic acid, and from glacial acetic 

 acid to xylene which is used to wash the 

 acetic acid from it. When all the acid has 

 been removed the specimen is transferred 

 to a weak solution of Canada balsam in 

 xylene, in which it remains until it is 

 thoroughly impregnated. 



A deep cell (see Chapter 1) is next ce- 

 mented to a glass shde, and the specimen 

 transferred to the cell which is filled to the 

 brim with a solution of balsam in xylene. 

 This is placed in the desiccator to evapo- 

 rate, the cell being filled up as often as is 

 necessary. The cell, with its contained in- 

 sect, is then slowly heated to drive off the 

 remainder of the solvent and finally closed 

 with a covershp. The writer must again 

 confess, reluctantly, that such specimens 

 make magnificent show pieces that are 

 of very doubtful scientific value. 



Preparation of an Alga in Venice Turpentine 



Venice turpentine is the natural balsam cidua). It is a thick balsam, of about the 

 which is exuded by the larch {Larix de- consistency of natural Canada balsam. 



