TlIK AMERICAN MONTHLY |.I:i:ni!uy. 



Mh Kosroi'u AL .vrrviJAii s. 



An Excellent Mounting Medium. — DIssdIm- «;iiin (l;mi;ii in 

 bcn/.ol to the consistency ot" a tliin syrup. (»cl rid of the l;ii«:jcr 

 particles of tlirt l>v straininj; throui^li an old silk lianilkercluef, 

 and add to the cohite about one-tliiid of its vohnne of lii|Uor 

 potassa'. Shake until inixeii, cork well, and set aside in a warm 

 place for several weeks. On exanvination the mixture will he 

 toiMul t«) have se|)arated into two la\ers, the lower of which (a 

 resin soap i will contain all the impurities, the upper consisting 

 of pure neutral damar in hen/ol. Draw this ofl" anil to each 

 ounce add about S or lo dro|)s of poppy oil. This latter prevents 

 the brittleness which the ihv damar naturally possesses. The 

 mounting; medium thus prepared is too thin for immediate use, 

 but this is easily remedied by leavinj^ the bottle open or loosely 

 corked in a warm place lor a day or two. If left open. cover the 

 top of the vessel with a bit of lint cotton or a linen raj^ to keep 

 out dust. — \ii(i(>na/ /fr//i;'^>/s/. Dcccnihcr /. iSgj. 



A Nearly Colorless Damar. — Dissolve the damar in benzol 

 anil make suthcientl} thin to tiltcr readilv through paper in a closed 

 filter. Filtration may be avoided, if you have plenty of time, by 

 adilin«j zinc oxide. shakin<; well, and allowintr to stand until the 

 oxide settles to the bottom. carrvinj2f all foreign matters with it. 

 The oxide should be wet with benzol before adding it, to insure 

 its thorough incorporation. Filter or decant, as the case may 

 be, and to the filtrate add alcohol in small quantities until the 

 addition no longer causes a precipitate. Filter oH' and wash the 

 precipitate with absolute alcohol two or three times, and then 

 dry- The result will be a white, finely divided powder, which, 

 when thoroughly drv, is dissolved in crvstallizalile benzol, giving 

 a colorless or nearly colorless solution. This solution evaporated 

 leaves a colorless but excessi\ely brittle layer of resin. The 

 brittleness may be corrected by the addition of poppy oil. Thus 

 prepared the medium is practically colorless and has a high re- 

 fractive index. The residual alcoholic mixture rapidly clears 

 itself on standing, and on evaporation leaves a tenacious but 

 slowlv (Irving gum that makes an excellent cement basis — 

 National Druggist. Dcccttibcr I. iHi)i. 



Use of Compressed Carbonic Acid Gas for the Freezing 

 Microtome. — A method which has been in use in the Sears 

 Fatliological Laboratory of Harvard Medical School for over two 

 vears is described bv Dr. Frank B. Mallorv in the Boston Med- 

 ical and Surgical Journal . This gas, carVjon dioxide, is prefer- 

 able to ether or to rhigoline for freezing. The '' liquid carbonate " 

 of commerce is obtained from the American Carbonate Co., 424 

 E. 19th street. New York, in cylinders of 10 or of 20 pounds each, 

 but some slight modifications are needed to adapt their cylinders 



