INTRODUCTION. 23 



This is easily effected by first saturating the object with alcohol 

 (beginning preferably with dilute, and then using stronger), in 

 order to expel all water ; next placing the alcoholic specimen 

 in oil of cloves, turpentine, or benzol, until the alcohol is in 

 turn expelled. The specimen thus permeated is transferred to 

 balsam which has been previously placed on the slide. Care 

 must always be taken to have the balsam perfectly free from 

 air-bubbles. 



111. When used alone, the balsam on the slide ma}' bo 

 heated, to drive off a part of its more volatile constituents, and 

 the specimen can then be placed in the warm liquid. But this 

 method is not applicable when the specimen is affected by slight 

 heating ; it is best adapted to hard tissues, like woods and fibres. 

 Balsam which has thus been heated hardens on cooling to a good 

 degree of firmness. This firmness is secured with balsam used 

 without heat only after a longer lapse of time, during which the 

 more volatile matters have escaped. 



112. If pure balsam is cautiously heated in a capsule until it 

 no longer gives off vapors, the melted mass will cool into a pale 

 amber-colored solid. This solid dissolved in a small quantity of 

 benzol forms a liquid of the consistence of syrup, which is useful 

 for all mounting where heat is injurious. The specimens must 

 be treated successively with alcohol and benzol, and the}' are 

 then ready to be immersed in the benzol-balsam on the slide. 

 An equally serviceable solution is made by dissolving the mass 

 in chloroform. Chloroform-balsam requires the specimen to be 

 saturated with chloroform before immersion. 



113. In all the above cases two precautions will save disap- 

 pointment : 1st. the slides and cover-glasses should be heated 

 slightly, to drive off any moisture on the surfaces which are to 

 come in contact with the mounting-medium ; 2d. the covers 

 should be held in place by means of a slight weight, or by the 

 pressure of a spring clip, until the balsam or its solution has 

 become tolerably firm. A little experience will show that speci- 

 mens mounted in balsam may require a somewhat different 

 management of the mirror under the stage from those which are 

 mounted in a medium with a different refractive power. Damar 

 may replace balsam when the latter, which is the better, is not 

 to be had. 



114. Hoyer's mounting-media are highly recommended by 

 Strasburger. ' The one which is preferred for anilin preparations 



1 Das botan. Practicum, 1884, p. 40. 



