MOUNTING OBJECTS IN CANADA BALSAM. 21? 



hausting process two or three times ; and in this case it is prefer- 

 able to use Camphine or Oil of Turpentine instead of balsam, on 

 account of its greater fluidity, and to warm even this to a tempera- 

 ture of about 100°. — There are certain cases, on the other hand, in 

 which it is desirable to retain, instead of expelling, the Air contained 

 within the cavities of the object. Thus, if minute Insects (such as 

 Fleas) be displayed as transparent objects to show the ramifications 

 of the Trachea?, or if it be wished that a section of Tooth or Bone 

 should be so mounted in balsam as to exhibit its canaliculi, the 

 previous maceration in Oil of Turpentine should be never employed, 

 and the Balsam employed should be some which has been previously 

 hardened ; this being melted without the use of more heat than is 

 necessary, the object should be surrounded by it and the cover put 

 on as quickly as possible ; and the slide should then be laid upon 

 a surface of stone or metal, the good conducting power of which, 

 by causing the balsam to cool rapidly, diminishes its tendency to 

 penetrate the substance of the object. — If a deep cell has to be filled 

 with Canada Balsam, it is better to fill it in the first instance with 

 Oil of Turpentine, and to immerse the specimen in this ; liquid 

 balsam being poured upon the object at one end, the Turpentine is 

 to be allowed to flow out at the other by inclining the slide ; then 

 by laying the glass cover on one edge of the cell, and gradually 

 lowering it until it lies flat, air may be entirely excluded. 



161. When the Object is already attached to the Glass slide, the 

 mounting in Canada Balsam is usually a matter of very little diffi- 

 culty. If it be a soft tissue which has been spread-out and allowed 

 to dry upon the glass for the purpose of securing it in its place, all 

 that is necessary in the first instance is to dry it thoroughly, to shave 

 or scrape it with a sharp knife if it should seem too thick, and to 

 moisten its surface with Oil of Turpentine if it should not readily 

 ' take ' the balsam. The slide is then very gently warmed, a 

 sufficient quantity of Balsam is spread over the surface of the speci- 

 men, with due cax*e that it is ' taken ' in every point, and the glass 

 cover is put-on. If the preparation cover a large area, great care 

 shoidd be taken in letting-down the cover gradually from one side, 

 so as to drive a wave of balsam before it which shall sweep away 

 air-bubbles ; raising it a little, and introducing a small quantity 

 of fresh balsam, if any vacuity present itself as it descends. — The 

 preferable mode of mounting thin sections of hard bodies, however, 

 will depend in great degree upon the size of the section and the 

 tenacity of its substance. "Where its area is great and its texture 

 brittle, its removal from the glass on which it has been ground-down 

 to another slip cannot be accomplished, even by the most dexterous 

 management, without considerable risk of breaking it ; and al- 

 though, by the friction of the glass upon the stone, the surface of 

 the slide will probably have been scratched or roughened, yet this 

 is a dis-sight about which the scientific Microscopist will care but 

 little, as it only affects the saleable value of such objects. Nothing 



