324 THE AMERICAN MONTHLY [Nov 



placed on the slide, the object worked iuto it as before. If 

 necessary another drop of balsam is added, and then the 

 cover-glass is gently lowered and pressed down. If the 

 cover-glass is lowered with one edge first it carries air- 

 bubbles away more readily, but it also has a tendency to 

 displace the object. The beginner will find that at first 

 he uses either too much or too little balsam, but he will 

 soon learn to judge this. Excavated cells, which are used 

 for thick objects, but for those not thick enough to re- 

 quire an actual cell, are rather troublesome at first, as, un- 

 less there is balsam sufficient to completely fill the cell, an 

 air-bubble will be found under the cover-glass, and it is 

 not always easy to get rid of this without displacing 

 everything. 



Mounting in Glycerine Jelly. — This is simpler than 

 mounting in Canada balsam, and the preparation before- 

 hand is also simpler. The object must be well soaked in 

 water, and every trace of alcohol, turpentine, etc., got rid 

 of. Owing to the fact that glycerine jelly does not absorb 

 air-bubbles like Canada balsam, it is well to soak in water 

 that has been recently boiled for about ten minutes and 

 allowed to cool. The steeping is preferably done in a stop- 

 pered bottle or jar. Prolonged soaking in water is a great 

 aid in getting rid of air-bubbles embedded or entangled 

 in the object, and will generally prove effectual without 

 the aid of an air-pump. It is advisable to soak finally in 

 a mixture of glycerine and water, say one-third of the for- 

 mer, before mounting. The process of mounting is car- 

 ried out as follows : The slide is placed on the brass ta- 

 ble, the object is transferred to its centre by means of the 

 section-lifter, and any excess of water removed by the 

 edge of a bit of blotting-paper, care being taken that the 

 latter does not come in contact with the object itself. By 

 means of the point of a knife, a small spatula, or other sim- 

 ilar instrument, a small portion of glycerine jelly is then 

 placed on the object, the requisite quantity being easily^ 



