148 



THE AMERICAN MONTHLY 



[August, 



mounting small objects in cells, part- 

 ly because some of them, particular- 

 ly salicylic acid, cause a rapid change 

 of color of such preparations as algae, 

 but mainly because they are not ne- 

 cessary as preservatives. Water alone 

 is quite sufficient, probably because 

 it takes Up sufficient alcohol or other 

 substance from the cement used in 

 attaching the cover-glass to prevent 

 any growth within the cell. 



We will now proceed to give a gen- 

 eral description of the processes of 

 mounting in a cell in fluid, and al- 

 though it has been quite commonly 

 supposed that fluid mounts are not 

 durable owing to the difficulty of seal- 

 ing them, we hazard the assertion that 

 those who will follow the directions 

 here given will never be troubled w^ith 

 imperfect cells. These directions 

 must be followed in every detail or 

 we cannot guarantee good results. 

 For convenience we number the op- 

 erations in order. 



Mounting in Aqueous Fluids 

 AND Glycerin. — i . Prepare a num- 

 ber of slides with cells of thick shel- 

 lac of the proper depth for the speci- 

 mens, and let the shellac be thorough- 

 ly hard before mounting. The best 

 method of preparing deep cement 

 cells is to use the shellac as thick as 

 it will readily flow from the brush, 

 and run a rather heavy ring on the 

 slide in the usual way, making the 

 inside diameter the exact size desired 

 for the finished ring. Then running 

 the turn-table rapidly, apply the point 

 of a knife-blade to the outside of the 

 circle and slowly move it inwards, 

 thus turning up the cement and in- 

 creasing the thickness of the ring. 

 With a very little practice cement 

 cells can be made a sixteenth or a 

 tenth of an inch deep in this way, 

 and very rapidly. Have the objects 

 ready, in the medium.in which they 

 are to be mounted, and then prepare 

 the hardened cells as follows : — 



2. Selecting a clean cover-glass, 

 run a coating of Canada balsam in 

 benzole with a brush on the top of 

 the cement-cell, being careful to cover 



it well with the balsam in such a way 

 that the cover-glass when applied will 

 sink down upon the balsain and ef- 

 fectually close the cell. 



3. Before the balsam has time to 

 harden, fill the cell with the mount- 

 ing fluid, transfer the object to it, ar- 

 range the specimen with care, and 

 immediately apply the cover-glass. 

 If the object be one that is easily dis- 

 arranged, it will require considerable 

 skill to apply the cover without dis- 

 turbing it. This, however, must be 

 left to the ingenuity and skill of the 

 preparer, as it is impossible to give 

 directions that will immediately im- 

 part skill that only practice can give. 

 It may be said, as an indication of the 

 manner of putting on the cover-glass, 

 that the cover should be held in for- 

 ceps in the right hand while a needle 

 in the left will sei-ve to direct it to the 

 proper place on the cell. One edge 

 of the cover is placed on the cell 

 against the needle point, which pre- 

 vents it from slipping, and the other 

 side is then gradually lowered, driv- 

 ing out the superfluous fluid beneath 

 it, until it rests in position. In do- 

 ing this, breathe upon the cover, so 

 that the moisture of the breath may 

 condense upon the under surface. 

 This causes the fluid to come readily 

 in contact with the cover, and pre- 

 vents the inclusion of bubbles of air. 

 Then gentle pressure is applied 

 around the edges to ensure perfect 

 contact, and the superfluous fluid is 

 removed from the slide with blotting- 

 paper, except when the fluid is gly- 

 cerin, in which case it is generally 

 advisable to postpone any cleaning 

 until the balsam dries. 



The balsam cements the cover to 

 the cell, and if the sealing up to this 

 point is perfect the fluid will keep 

 for any length of time, so long as the 

 slide is not roughly handled. To en- 

 sure against any possible defect in 

 this respect, as soon as the balsam is 

 hard the slide is carefully dried, first 

 washing oft' every trace of glycerin 

 with water and a soft brush. 



4. A second coat of the balsam so- 



