ON COUNTING OBJECTS. 109 



the objects in a bath of turpentine, and then exhaust it 

 under the air-pump before applying the Canada balsam. 

 The limpidity of the turpentine allows of the free escape 

 of air, and when the object is removed from the bath to 

 be mounted, the balsam blends with the turpentine, and fol- 

 lows it into the minute cavities whither it could not alone 

 have penetrated. This turpentine bath is most useful for 

 killing insects, and possesses the advantage of making them 

 protrude their probosces, lancets, &c. ; they are rendered 

 more transparent than after killing by other means. If 

 it is intended to dissect out any part, then Swammerdam's 

 plan of suffocating in spirits will perhaps be more suitable. 

 But the best plan is to touch the mouth and spiracles of 

 the insect with a pencil dipped in creosote ; this has also 

 a preservative effect, and equally with spirit possesses the 

 advantage of hardening the viscera, which tends materially 

 to aid in their dissection, at least so long as the albuminous 

 portions are not very much coagulated, so as to cause the 

 delicate organs to adhere together. 



Mr. Boys says : " For mounting objects in Canada 

 balsam, the first thing to be considered is the apparatus 

 required. 



" 1st. A small single-wick oil-lamp, having a glass 

 chimney about four inches long; the name to be about 

 the size of that in a hand-lantern : a spirit lamp will do 

 even better. 



" 2d. Slips of glass of required size, and small pieces of 

 thin glass to cover the object, all well cleaned. 



" 3d. A pair of nippers to hold the glass slips. 



" 4th. A pointed iron piercer in a wooden handle. 



" 5th. A bottle containing the clearest Canada balsam, 

 diluted with the best spirits of turpentine to a consistency 

 allowing it to drop readily from one end of the iron piercer, 

 or Mr. Gorham's cementing pencil. The preceding articles 

 being spread before you ready for use, and the object to be 

 displayed well examined for choice of position, and cleaned 

 if necessary, fix the glass slip in the nippers, dip the piercer 

 into the balsam, and withdraw a full -sized drop to place 

 upon the slide. The centre of the slide should now be 

 rested across the chimney of the lamp until the balsam 

 begins to spread, when it must be immediately withdrawn. 



