3^4 



SCIENCE. 



slide, and the solution thus becomes useless for mount- 

 ing. 



Having cleaned his slides and covers, and having his 

 balsam solution prepared, the student may now proceed 

 to mount the objects in the following way : Place one of 

 the stained sections which have been kept in alcohol in 

 a small shallow dish containing some absolute alcohol, 

 and allow it to remain there for seme minutes, so as to 

 remove all traces of water which may iemain in it from 

 the staining fluid and which have not been removed 

 by the washing in the weaker alcohols. Then flcat it 

 on the surface of some oil of cloves, also contained in a 

 shallow glass or porcelain dish, until it has become 

 transparent, when it shculd be remcved from the oil, 

 spread out on a glass slide and covered with a thin cover 

 glass which has been taken from the bottle filled with 

 alcohol and wiped dry with a soft rag. The specmen 

 is now ready to be examined under the micioscope, in 

 order to see whether it will pay to permanently mount 

 it in balsam. If found good the cover glass is carefully 

 removed and all supeifluous oil remaining on the section 

 and on the slide is taken up with the edge of a piece of 

 blotting paper, the object covered with a drop of the bal- 

 sam solution, a fresh, dry cover is placed upon it, taking 

 care to exclude any air bubbles, and pressure is made 

 upon the cover to press out all superfluous balsam. In 

 order to prevent the formation of air bubbles in the speci- 

 men the cover shculd be held by the forceps, near the 

 edge, the opposite edge should be carefully placed into the 

 balsam and the cover gradually lowered over the section 

 until it lies flat upon it. If, after pressing the cover 

 down, it is found that the balsam does not extend to the 

 edge of the cover all round, a small drop of balsam 

 should be placed near the edge, at the point where the 

 balsam under the cover joins the empty space, when it 

 will run in by capilliary attraction. The slide is then 

 laid aside to allow the balsam to dry spontaneously, 

 which will take place in from four to six weeks, or it may 

 be placed in a drying oven, the temperature of which is 

 not raised above 130 F., when it will be ready for finish- 

 ing in a much shorter time. An excellent apparatus of 

 this kind is sold by dealers in microscopical appliances. 

 It consists of a box of copper containing movable trays, 

 surrounded by another larger box, also of copper, so that 

 a space remains between the two boxes, which, when the 

 oven is used, is filled with water through an opening at 

 the top. A thermometer is inserted through this open- 

 ing, and a lamp is placed under the outer box, which 

 raises the temperature of the water up to any desired de- 

 gree, and thereby warms the air in the inner box. A 

 current of air is established through the inner box by 

 ventilators, both at the top and bottom. Specimens 

 which have been double stained with indigo should not 

 be exposed to either heat or sunlight, as they will fade 

 under these circumstances. 



The fact that the oil of cloves or other volatile oils 

 which may be used in its stead shrink many ot the more 

 delicate tissues, and the difficulty attending the removal 

 of large thin sections from one solution to the other, as 

 well as the danger of tearing while they are spread upon 

 the slide, has led the author to discard the oil of cloves 

 as a clearing agent, and to adopt a plan of mounting in 

 balsam, which avoids all these dangers and which has 

 the advantage that the slides may be finished imme- 

 diately. 



MOUNTING IN BALSAM. 



After one of a number of sections which have been 

 stained together has been examined in oil of cloves, and 

 has been found to be good, the others may be inferred to 

 be also good and worth mounting. One of them is 

 placed in absolute alcohol, and after it has remained 

 therein for some time, is floated upon a cover glass, 

 which need not be wiped dry after taking it from the 

 bottle of alcohol in which the covers are kept, held in a 



pair of forceps whose ends have been bent so as to stand 

 at right angles to the shafts, and to close on top of 

 each other. The cover with the section on it is then 

 lifted out of the alcohol, when the specimen will be 

 found to be evenly spread out, needing but little unfold- 

 ing at the edges, which sometimes fold over; the lower 

 surface is to be wiped dry and a drop of the alcoholic 

 solution of balsam is placed on the section, which, on the 

 cover, is set aside in a place free from dust, to clear up 

 and allow the balsam to get dry. After fifteen or twenty 

 minutes another drop of balsam should be placed upon 

 it, in order to prevent the drying of the tissue. After 

 twelve hours the balsam has dried sufficiently on the 

 cover so that the specimen can be mounted, in the fol- 

 lowing manner : Take the cover up with a pair of 

 forceps and place a drop of crude berzole* on the bal- 

 salm and quickly place the cover, with the balsam down, 

 on a clean slide, as near the centre as possible, and 

 taking care to avoid air bubbles. Then warm the slide 

 over a spirit lamp, place on a turn-table and quickly 

 centre the cover so that its edge does not seem to shake 

 when the slide is rapidly revolved. Next run a ring of 

 cement around the edge, as will be described presently, 

 and then press gently upon the cover, to cause the sec- 

 tion to lie flat, and to press out the surplus of balsam, 

 which, with a little management of the pressure, will run 

 into the ring of cement. Another ring of cement may 

 then be applied, when the slide is ready to be labeled 

 and put away. 



The cement for balsam mounting which is most satis- 

 factory was devised by Mr. T. W. Starr, of Philadelphia, 

 and is prepared as follows : 



Clear Canada balsam, 370 grains. 

 Deodorized benzine, 140 grains. 

 Spirits turpentine, 120 grains. 

 Gum dammar, 185 grains. 



Mix the balsam and benzine well together in a bottle, 

 then add the turpentine and shake until mixed; finally, 

 add the gum dammar, in selected pieces, and shake fre- 

 quently till dissolved. If necessary, the solution should 

 be filtered through absorbent cotton, previously moist- 

 ened with turpentine. A portion of this is to be placed 

 in a small glass-capped vial, to the cap of which is 

 attached a small sable brush, which will come to a point, 

 the ordinary camel's hair brush not being suitable for 

 ringing, as it spreads too much. If the solution is too 

 thick to flow readily it should be diluted with spirits of 

 turpentine until the proper consistency is obtained. This 

 fluid is also an excellent mounting medium when the 

 object has previously been cleared in oil of cloves or 

 turpentine. For ringing, ^his cement may be colored 

 by adding to it a few drops of alcoholic solution of ani- 

 line of any shade desired, or it may be mixed with white 

 zinc, when the resulting ring will appear as if made of 

 porcelain. 



The specimen to be ringed is placed upon the turn- 

 table, and if any balsam has soiled the slide or the cover 

 it must be removed by scraping with a sharp knife and 

 afterward wiping with a soft linen rag wet with benzole. 

 Asa matter of course, the balsam should be hard, so that 

 ihe cover will not be displacad by the scraping and 

 wiping. If the cover should not be in the centre, and a 

 self-centering turn-table is used, the slide is to be 

 warmed until the balsam becomes soft, when the cover 

 may be centered on the turn-table. Having thus pre- 

 pared the slide, the brush in the cement bottle is removed 

 and the surplus scraped off, so that it is almost dry ; 

 with the left hand the turn-table is spun round rapidly 

 and the point of the brush applied to the edge of the 

 cover for a moment only, holding the brush slanting in 



*Thc refined benzole or benzine, which is frequently sold for benzole, 

 is to volatile for our purposes. . • 



