1884.] 



MICROSCOPICAL JOURNAL. 



Ill 



jects for the microscope will quickly 

 pick up numerous little ' (lod<2^es ' 

 which would only make these arti- 

 cles coiitusiiif:^ should we attempt to 

 describe them. The jj^reat fault in 

 most books on mounting seems to be 

 that the instructions are given too 

 much in detail. Cements are de- 

 scribed and recommended which the 

 authors perhaps have never seen, and 

 methods which no practical worker 

 would spend the time to carry out. 

 We prefer to write only of what we 

 have tried and know to be satisfac- 

 tory. It will be observed that we 

 have not given any elaborate method 

 of cleaning cover-glasses. This is 

 because the simplest method of all, 

 rubbing with a soft cloth between the 

 fingers, is quite sufficient. This is 

 rank heresy — but it is true neverthe- 

 less. 



Among the objects well suited for 

 mounting in glycerin-jelly may be 

 mentioned delicate vegetal^le tissues, 

 sections of plant-stems or leaves, veg- 

 etable fibres, alga;, pollen-grains, del- 

 icate insects mounted whole without 

 pressure, and numberless other ob- 

 jects. In fact this medium is more 

 universally adapted to mounting than 

 Canada balsam, which is much more 

 frequently used. The reader may 

 compare the two media — glycerin- 

 jelly and balsam — by mounting a thin 

 longitudinal section of a match in 

 each, and placing the two prepara- 

 tions under the microscope. The 

 advantages will be clearly seen in 

 favor of the jelly for such specimens. 



Mou?itinj^ in Resinous Media. — 

 Canada balsam is the one medium 

 most universally used of all the resi-. 

 nous compounds known. A number 

 of others have been recommended 

 from time to time as substitutes for 

 Canada balsam, but of these only gum 

 dammar has ^et been largely used. 

 vStorax bids fair to come into use 

 for certain purposes.* As all the 

 resinous substances are used in the 

 same way, only Canada balsam will 

 be particularly referred to here. 



* Vol. V, p. 69. 



Objects to be mounted in Canada 

 balsam must be specially prepared in 

 order that the balsam shall thoroughly 

 permeate them. Only very thin speci- 

 mens which have no tendency to re- 

 tain air within their pores or reticula- 

 tions can be prepared by thorough 

 drying alone. In all cases it is well, 

 even with such specimens, to first 

 saturate them with a drop of spirits 

 of turpentine, and then apply the bal- 

 sam. The turpentine penetrates every 

 part of the object, and the balsam fol- 

 lows it readily. There are many ob- 

 jects, however, which retain the air 

 so obstinately that when once they 

 are dried it is almost impossible to 

 remove it. This will be found the 

 case with many sections of vegetable 

 growths, but especially with prepara- 

 tions of insects. Such specimens 

 must not be allowed to become dry, 

 but the water which they contain, 

 which does not mix with balsam, must 

 be removed in another way. Or- 

 dinarily it can be successfully done 

 by meany of alcohol. Place the prep- 

 aration in common alcohol and allow 

 it to remain for several hours. Then 

 transfer it to strong alcohol,* which 

 removes the water so thoroughly that 

 the preparation may be placed in oil 

 of cloves w^ithout causing turbidity. 

 Oil of cloves, oil of cajeput, or euca- 

 lyptus oil may be used. They clear 

 the specimens and replace the alco- 

 hol. In a short time, depending upon 

 the density and size of the specimen, 

 the oil will have penetrated every 

 part, when the specimen may be 

 placed upon a slide and mounted in 

 balsam in the manner to be described 

 further on. The usual practice is to 

 transfer specimens from oil of cloves 

 to turpentine or benzole before put- 

 ting them into balsam. Some objects, 

 especially sections of plants, shrink 

 badly in either of these media, and it 

 is quite possible to mount them di- 



* English books say ' absolute alcohol,' 

 but this is not necessary, and in convers- 

 ing with preparers in England we learned 

 that they applied the name absolute alco- 

 hol to strong alcohol. 



