1884.] 



MICKOSCOPICAL JOURNAL. 



133 



as described on page 73 1 and this is 

 then lowered upon a drop of balsam 

 on the slide. To mount diatoms /// 

 situ on algtc in balsam, which, in the 

 case of Isthmia^ Arachnoidiscus^ 

 Achnanthcs^ and other large forms, 

 is sometimes a very excellent plan, 

 yielding fine slides for dai-k-field illu- 

 mination, a method recommended by 

 the late Charles Stodder, is very good. 

 Place the specimen in chloroform and 

 see that the fluid fills all the diatoms 

 and drives out the air. Then trans- 

 fer them to a slide with considerable 

 of the chloroform, and before this has 

 time^to evaporate drop on suflicient 

 balsam dissolved in chloroform to 

 cover them. jAs the chloroform evap- 

 orates, the balsam takes its place and 

 fills the interior of all the frustules. If 

 air bubbles remained within the latter, 

 their beauty would be much marred. 



It is often required to mount ob- 

 jects in balsam which require cells 

 more or less deep. Thus, the beauty 

 of the elytron of the gorgeous dia- 

 mond-beetle is very much enhanced 

 by mounting it in balsam as an opaque 

 object. It requires a deep cell, which 

 may be made^with a glass ring ce- 

 mented to the slide with any trans- 

 parent cement — balsam is as good as 

 any. A very neat mount, however, 

 may be made by turning up a cell 

 with benzole balsam in the manner 

 to be described under mounting in 

 fluid. When such a cell is well 

 hardened it may be filled with soft 

 balsam without danger of itself be- 

 coming softened, and when the mount 

 is completed it will appear like a 

 solid mass of balsam, no cell being 

 visible. Such a mount must be al- 

 lowed to harden without artificial 

 heat. The balsam will soon harden 

 outside, but the interior portion will 

 remain soft for years. The reader 

 will recall an article on this subject 

 published in the May number, p. 84. 



A very excellent method of mount- 

 ing in balsam is known as the car- 

 bolic acid process.* This is espe- 



* Vol. i. p. 161. 



cially adapted to the mounting of 

 whole insects without pressure. The 

 insect is dropped alive into the strong- 

 est aqueous solution of carbolic acid. 

 In a short time it becomes permeated 

 with the fluid, when it may be trans- 

 ferred directly to raw balsam in a 

 cell. 



The use of hard balsam dissolved 

 in benzole or chloroform is much in 

 favor with some mounters. For our- 

 selves we generally prefer the raw 

 balsam that has been hardened by 

 long keeping and bleached by expo- 

 sure to the sun. This, however, is 

 probably merely a matter of habit, 

 and the dissolved balsam soon hardens 

 on the slide without heat, or the 

 mount may be finished in a few mo- 

 ments over a lamp. On the other 

 hand, there is much shrinkage in vol- 

 ume of the balsam solution in drying, 

 and, when the preparations are put 

 aside to harden, the balsam is very 

 likely to shrink beneath the cover- 

 glass, leaving a vacant space to be 

 filled up at some future time. More- 

 over, balsam hardens in time so as to 

 become quite brittle, and old balsam 

 mounts will frequently allow the 

 cover-glass to fall ofi' with the slight- 

 est jar. This danger is more likely 

 to occur with those mounts prepared 

 with hardened and dissolved balsam, 

 for the reason that the volatile solvent 

 soon passes oft', leaving the resin hard 

 throughout, while a mount made with 

 raw balsam may remain more or less 

 soft within for many years. 



Dissolved balsam, however, pos- 

 sesses some advantages for certain ob- 

 jects. For example, in mounting 

 small foraminifera or polycystina the 

 dry specimens may be placed on 

 a slide, a few drops of the balsam in 

 chloroform added, the cover-glass laid 

 on, and the slide warmed over the 

 spirit-lamp until the chloroform boils 

 briskly. The air is thus driven out 

 from the shells, and a good mount 

 can be finished in a few moments. 

 It is also thought that in mounting 

 stained vegetable preparations the 

 benzole balsam is to be preferred, as 



