102 MICROSCOPIC OBJECTS. 



majority of transparent objects may be mounted. Most in- 

 sects and the parts of the same are mounted in balsam ; 

 they must be placed in the potassa solution from six hours 

 (or less) to as many days, according to the softness or 

 hardness, or transparency or opaqueness, of the object ; ex- 

 perience will give the time. They must then be put under a 

 slight pressure so as to squeeze out part of the extraneous 

 matter ; replace in the potassa solution for a short time, then 

 put them under increased pressure until cleared of the rest of 

 the contents, when they must be placed in a large quantity of 

 warm water for a few hours. It is best not to touch the object 

 at this stage even with a camel-hair brush ; but the vessel of 

 water must be repeatedly shaken and extra water added, so as 

 to thoroughly clean the specimen from the potassa (this is 

 important) ; it must then be taken out of the water and dried 

 between two slips of glass. All the pressure requisite for 

 a small object is obtained by the use of the American 

 paper-clips ; but if the object is large and thick (as, e.g., 

 many of the beetles), the regulated pressure of a small 

 screw-press is necessary. After it has been well dried 

 (which, of course, will take from a few hours to as many 

 days, according to the size and nature of the object) it 

 must be soaked in turpentine, or, what is better, distilled 

 Canada balsam, until moderately transparent ; if small, it 

 must not be taken from the glass slide. A slip of glass of 

 the recognized size, 3x1 inches, must be taken, a drop 

 of balsam (the size of the drop proportionate to the size 

 of the object) placed with the glass tube in the centre of the 

 slide ; the drop must then be made to spread slightly by the use 

 of moderate heat, the object placed in it, arid the thin glass 

 cover applied with care. If any air-bubbles appear, they will 

 generally be found to have dispersed after a day or two ; and un- 

 less the object is valuable, it is best never to attempt to 

 remount it. As the patience of the learner would be greatly 

 tried during the process, it is always better to begin again 

 with a fresh specimen. The balsam takes a long time to dry if 

 left to itself, which is best ; but if the objects are wanted 

 early, they may be dried over a gas-jet, or by any other plan, so 



