1890.] MICEOSCOPICAL JOURNAL. 251 



that arising from the presence of air-bubbles ; but this liability can be 

 overcome by placing the object to be mounted on a small portion of 

 Canada balsam, previously put on the slide, and then dropping another 

 small portion on the centre of the cover-glass, and upon bringing the 

 two carefully together with the aid of the forceps, the air is excluded. 

 While Canada balsam is an extremely useful agent in various degrees of 

 age and hardness as a mounting medium, it will be found more useful if 

 thoroughly hardened and redissolved. Take it as supplied by dealers, and 

 pour it into a glass and evajDorate it by heat, till, upon dropping a little 

 into cold water it is found to set hard like a piece of resin ; it may then 

 be set aside to cool, when it is ready for solution. Two solvents have 

 been recommended — chloroform and benzole. Of these two the author 

 prefers the latter, and advises its use because after solution in this it be- 

 comes very limpid and colorless, any foreign matter in it soon settling 

 to the bottom. It should be kept for use in a capped bottle, and it 

 after a time it should become stiller, it maybe diluted with a little ben- 

 zole. One great advantage of this solution is the readiness with which 

 air-bubbles in it disappear after a few hours. The slide and preparation 

 may be plentifully covered with them, but they soon become absorbed, 

 and finally the preparation is quite free from them. 



Glycerine Jelly ^ a very uncertain preparation ; after a time large air- 

 spaces develop in it, probably the result of desiccation. The object to 

 be mounted must be previously well soaked in glycerine. Air-bubbles 

 are very liable to accompany its use, and they are difficult to get rid of 

 by reason of the tenacious character of the glycerine. 



While Canada balsam and glycerine jelly readily lend themselves to 

 the mounting of such preparations as are substantial in their character, 

 as are the sections of different tissues, hard and soft, there are other 

 preparations as dissections of insect anatomy and delicate objects, both 

 animal and vegetable, which would be crushed out of all recognizable 

 shape by the pressure necessary in lusing such comparatively hard 

 mountants as these ; therefore recourse is had to fluid preservative 

 media, to which attention may now be directed. 



In using these it is well to bear in mind the necessity of considering 

 the density of the fluid medium, that it bear a proportionate relation 

 to that of the preparation to be mounted ; for instance, a delicate ob- 

 ject, especially if of a tubular character, w^ould collapse and be crump- 

 led out of its proper shape and probably spoiled by being placed in 

 dense glycerine, but by altering the density of this by dilution the character 

 of the preparation can be preserved. Thus glycerine is a favorite 

 mountant from its adaptability to almost all objects, and the facility with 

 which it unites with other chemicals ; nevertheless, it needs discrimina- 

 tion in its use. It cannot be employed for calcareous tissues like bone 

 or shell, as they would become decalcified after being exposed to its 

 influence for some time ; therefore, for these preparations only balsam 

 should be used. Glycerine used in its full strength is highly refractive, 

 and is thus useful in bringing into view the minute details of many 

 structures. Objects to be preserved in dense glycerine should first be 

 soaked in a diluted solution and passed through solutions of increasing 

 density till that of the original glycerine is attained ; in this way all risk of 

 distortion is averted. Glycerine diluted with camphor water makes an 

 excellent preservative fluid ; but one which finds much favor with mi- 



