Practical Hints. 223, 



microscopist attempts to make the indigo solution himself. 

 But, even if it should prove so, the result obtained is well 

 worth the pains taken, and fully repays the outlay of time and 

 patience bestowed upon it. 



Mounting, 



The question as to the best material for permanently mount- 

 ing and preserving microscopical preparations is one of great 

 mportance, which fact is best illustrated by the existing con- 

 troversy between eminent microscopists as to the merits of 

 Canada balsam and glycerin as preserving media. My ex- 

 perience has taught me that, in most cases, pure Canada balsam, 

 dissolved in absolute alcohol, is to be preferred to any other 

 mounting material, but for a few tissues, and for special pur- 

 poses, glycerin is better. I do not intend, however, to discuss 

 this point here, but will give merely a short description of the 

 simplest methods of mounting in Canada balsam and glycerin. 



Balsam. — The specimen to be mounted is placed in Squibb's 

 absolute alcohol, so as to extract all traces of water which 

 might have been left in it from the staining fluid. It is then 

 removed, drained of surplus alcohol on the back of the hand, 

 and transferred to a shallow glass cup filled with pure benzol 

 (not benzine), which will speedily make it transparent. I pre- 

 fer benzol to oil of cloves or turpentine, for several reasons: 

 I, a specimen cleared in oil of cloves and then mounted in 

 balsam does not improve in distinctness by age as much as one 

 cleared in benzol, because the balsam cannot penetrate into 

 the interstices of the tissue perfectly and thus bring out its de- 

 tails; 2, because the oil causes the balsam to harden very 

 slowly, and 3, because the method of quickly mounting large 

 and thin sections, as described below, can not be employed as 

 well with the oil of cloves. 



Sections which need but little arranging on the slide, and 

 very young foetal preparations, are better placed in the 

 alcoholic balsam solution without first clearing them, as the 

 balsam will make them transparent, provided all water has 

 been extracted. After they have become transparent the ob- 

 jects are placed on a clean slide with sufficient balsam to cover 

 them, and the thin cover is laid on and pressed down. 



The Canada balsam solution mentioned above is prepared 

 according to Dr. J. J. Woodward's formula, as follows: A clear 



