128 D. E. GODDARD ON MANIPULATION WITH CANADA BALSAM. 



to digest them in solution of potassa, to soften hard structure, so 

 as to get the object as flat as possible. For some subjects this 

 mode of treatment may be required, but I have seldom used it. I 

 place small insects in camphine, and let them remain for months, 

 having previously perforated the abdomen. I find this advantage ; 

 the muscular structure is not destroyed, and insects prepared in 

 this manner present a very beautiful appearance by polarized light. 



I cannot help thinking that the application of heat by means of 

 a water bath, would effect a great saving of time in all prepara- 

 tions of this character, and be very useful in very many operations 

 connected with microscopy. 



There are three methods of applying the balsam. 



1. — Place the object on the slide, and let a drop fall on it. 



2. — Place a drop on the slide, and push the object into it. 



3. — Place the object on the slide, cover with thin glass, and drop 

 the balsam at the edge, and let it run in by capillary attraction. 



I do not pretend to say which of these is the best ; the student 

 will soon find out which is the most convenient and produces the 

 best results. 



Drying. — Having now noticed the preparation and mounting of 

 the specimen, the next question is, how is it to be hardened and 

 finished ? This is easy to ask, but not so easy to answer. Some 

 authorities advise placing the slide on the mantlepiece of a warm 

 room, some the use of an oven after the day's fire has gone out ; 

 many suggest a flat metal table, heated by a gas or spirit lamp, 

 and others again advocate the water bath ; I have tried each of 

 these methods. The first is only to be advised when the student 

 does not wish to finish his preparation for some long period, or 

 when, from the nature of the object, or the presence of air bubbles, 

 he wishes it to dry very gradually. The oven I have found very 

 inconvenient, and cannot recommend it, as the degree of heat can- 

 not be regulated with the precision that is necessary. The water 

 bath I consider infinitely preferable to a flat metal table ; both 

 these methods are, I think, open to the same objection. When a 

 flat metal surface is used, the centre of the slide comes in direct 

 contact with the heated surface, and the heat obtained, especially 

 from a flat table, is more than many structures will bear without 

 undergoing such alteration as will render them of little value to 

 the student, and unless the lamp is very carefully watched and 

 regulated, bubbles may arise at any moment and the balsam boil. 



