272 PREPARA TION OF REAGENTS [ CH. IX 



soluable in water were used as the denaturing substance, denatured alcohol 

 could be used in microscopic work for all the grades. That denatured as indi- 

 cated above can be used only in full strength or very slightly diluted. 



For educational and other public institutions the U. S. government grants 

 the privilege of using ethyl alcohol without paying the revenue tax, but for 

 private institutions and for individuals it would be a great relief if the dena- 

 tured alcohol could be mixed in all proportions with water without the forma- 

 tion of precipitates. 



\ 383. Balsam, Canada Balsam, Balsam of Fir. This is one of the oldest 

 and most satisfactory of the resinous media used for mounting microscopic 

 preparations. 



The natural balsam is most often used ; it has the advantage of being able 

 to take up a small amount of water so that if sections are not quite dehydrated 

 they will clear up after a time. 



\ 384. Xylene Balsam. This is Canada Balsam diluted or thinned with 

 xylene (xylol of the Germans). It is recommended by many to evaporate the 

 natural balsam to dryness and then to dissolve it in xylene. For some pur- 

 poses, e. g.: for mounting glycogen preparations, this is advantageous ; but it 

 is unnecessary for most purposes. Xylene balsam requires a very complete 

 desiccation or dehydration of objects to be mounted in it for the xylene is 

 immiscible with water. 



\ 385. Filtering Balsam. Balsam is now furnished already filtered 

 through filter paper. If xylene balsam is used it may be made thin and 

 filtered without heat. For filtering balsam and all resinous and gummy 

 materials, the writer has found a paper funnel the most satisfactory. It can 

 be used once and then thrown away. Such a funnel may be easily made by 

 rolling a sheet of thick writing paper in the form of a cone and cementing the 

 paper where it overlaps, or winding a string several times around the lower 

 part. Such a funnel is best used in one of the rings for holding funnels, so 

 common in chemical laboratories. The filtering is most successfully done in 

 a very warm place like an incubator or an incubator room. 



\ 386. Neutral Balsam. All the samples of balsam tested by the author 

 have been found slightly acid. This is an advantage for carmine, and acid 

 fuchsin stain or any other acid stain. Also for preparations injected with 

 carmine or Berlin blue. In these cases the color would fade or diffuse if the 

 medium were not slightly acid. For hematoxylin and many other stains the 

 acid is detrimental. For example, the slight amount of acid in the balsam 

 causes the delicate stain in the finest fibers of Weigert preparations to fade. 

 To neutralize the balsam add some pure sodium carbonate, set the balsam in a 

 warm place and shake it occasionally. After a month or so the soda will 

 settle and the clear supernatant balsam will be found very slightly alkaline. 

 Use this whenever an acid medium would fade the stain in the specimen. 



\ 387. Acid Balsam. As stated above all balsam is naturally somewhat 

 acid, but for various stains it is desirable to increase the acidity. For 

 example, specimens stained with picro-fuchsin, or injected with carmine or 



