132 



THE AMERICAN MONTHLY 



[July, 



should therefore be placed in an evap- 

 orating dish and heated very gently 

 — preferably over a water-bath in 

 ■which the water is not allowed to 

 boil — until it reaches a syrupy con- 

 sistence. When cold it will be thicker 

 than while warm, and it should be 

 tested by placing a few drops on a 

 cold slide and watching its behavior. 

 When it seems to be right the solu- 

 tion may be poured into a bottle and 

 about three drops of castor-oil added 

 for every ounce of solution. This 

 causes it to flow smoothly from the 

 brush. 



In practice we have found it ad- 

 visable to evaporate the solution, as 

 above described, until it is quite too 

 thick to flow from the brush, and 

 then to thin it with strong alcohol. 

 The reason is that during evaporation 

 the alcohol of the original solution is 

 driven off' more rapidly than the water 

 that is associated with it. Therefore, 

 by the time the solution is reduced 

 to one-fourth its original volume the 

 alcohol has become much weaker 

 than it should be, and the cement 

 dries slowly. By thinning the solu- 

 tion with strong alcohol the resulting 

 cement becomes all that can be de- 

 sired. 



It is well to have two kinds of shel- 

 lac cement always at hand — one so 

 thick that it will just flow from the 

 brush on the turn-table, the other 

 thinner. The first is useful for mak- 

 ing cells, the second as a general ce- 

 ment to attach covers, etc. 



Microscopical Technic. 



On page 92 we referred to a method 

 of making cells used by Mr. C. F. 

 Cox, concerning which a letter from 

 that gentleman appears in the corre- 

 spondence column of this number. 



It appears we were in error as to 

 the composition of the cement used 

 by Mr. Cox, and we can now under- 

 stand how the mistake came about. 

 This, however, is of no consequence 

 to the reader, as Mr. Cox's formvila 

 is now given in full. Munich lake, 



■which was mentioned on page 92, is 

 a good color, which dries hard, form- 

 ing an excellent cell of any required 

 depth, and ■we have used it for mak- 

 ing cells ■with perfect satisfaction. 



We may here depart from the strict 

 rule of these articles so far as to give 

 one process ■which ■we have not yet 

 tried, but which seems to possess 

 some advantages. Instead of trans- 

 ferring the object from strong alcohol 

 to oil of cloves it may be mounted di- 

 rectly in a solution of balsam in abso- 

 lute alcohol. This has been done 

 with specimens illustrating animal 

 histology, but ■we are not aware that 

 it has ever been applied to botanical 

 preparations. 



The operation of mounting most 

 objects in balsam is exceedingly sim- 

 ple. The speciinen should be ar- 

 ranged on the slide over the central 

 dot, ■with the turpentine or essential 

 oil,* as the case may be. The excess 

 of turpentine or oil mav be taken up 

 with a clean piece of bibulous paper, 

 and a drop of Canada balsam allowed 

 to fall upon it. By slightly heating the 

 slide the balsam replaces the oil and 

 pen-neates the object. A clean cover- 

 glass is then applied and the heating 

 continued until the cover glass is ■well 

 settled in place, aiding the operation 

 by means of the mounted needles. 

 If the object mounted will stand heat 

 ■well, the balsam inay be hardened 

 rapidly by heating on the mounting 

 table. Otherwise, the slide must be 

 placed in a -warm place ■where the 

 balsam may harden slowly^ When 

 it is hard around the edge of the cover- 

 glass the slide may be cleaned by 

 scraping oft" superfluous balsam with 

 a knife, and removing the last traces 

 with ammonia, alcohol, turpentine, 

 or any other solvent. 



We cannot give all the variations 

 to which these processes are subject, 

 but several methods for special pur- 

 poses deserve to be mentioned. Di- 

 atoms are dried upon the cover-glass, 



* Dr. T. Taylor has advised the use of 

 eucalyptus oil in mounting. See page 

 119, current volume. 



