280 Transactions of the Society. 



museum jars or specimen tubes after having had a second bath of 

 acetone ; this latter is poured off and one or other of the above 

 varations of tlie medium poured in. The specimen clears in a short 

 time, and any air-bubbles left can be removed by the application 

 of gentle heat, or, if very obstinate, by the use of an air pump. The 

 acetone used for the baths need not be discarded, as the moisture 

 can be removed by adding cupric sulphate, heated to white powder, 

 and then filtering. This method may be used with advantage for 

 specimens, such as mosquitoes, sent from abroad, which have been 

 preserved in formalin or alcohol. 



B. If one is dealing with small specimens or with wet or dry 

 cover-glass preparations, these, after stainicg. are takeil from any of 

 the grades of alcohol between 75% and absolute, placed on a slip and 

 covered with a cover-glass, filling up any sjtace left with the grade 

 of alcohol from which the specimen is taken ; if desired a higher 

 grade of alcohol or even acetone may be transferired between the 

 cover and slip ; then a drop of the selected mediuih, of such a con- 

 sistency that it will run easily, is placed at one edge of the cover- 

 slip, while, with a piece of bibulous paper the alcohol or acetone is 

 drawn off at tne opposite side, thus causing the medium to flow in 

 until it entirely replaces the alcohol or acetone. Usually a milky 

 cloudiness appears in the preparation if the medium is used to 

 replace 75% alcohol or methylated spirits, but this disappears if 

 t he slide is gently warmed and the cover-glass quickly raised from 

 its edge and lowered again. The best results are obtained when 

 the specimen has had a bath of absolute alcohol or acetone just 

 previous to the addition of the acetone balsam. Attempts to carry 

 the specimen direct from water or 5% formalin through an acetone 

 bath into the medium have so far met with no success ; yet I 

 believe that this may be possible if the absorbed water is extracted 

 from the acetone by placing some desiccating agent, such as fired 

 carbonate of potash (pearl-ash) or copper sulphate, in the bottom 

 of the vessel containing the acetone bath. 



As the medium penetrates the specimen, clearing simultaneous!}^ 

 takes place, in a manner similar to that which occurs when a 

 specimen is passed from alcohol through some of the essential oils. 

 The mount will harden in a few hours as the acetone gradually 

 evaporates, leaving the specimen embedded in a layer of Canada 

 balsam or other gum. Several slides mounted in a Bouin's Fluid 

 acetone-balsam medium have now been under observation for nine 

 months. They show no tendency to deteriorate, but rather indicate 

 the stability of the medium, there being no signs of precipitated 

 deposit, no discoloration of the medium, nor uneven shrinkage of 

 the specimen due to the drying of the balsam ; in fact, any shrink- 

 age which may occur is due rather, I think, to some fault in 

 fixation. 



