146 PREPARATION AND MOUNTING 



on which I fix my cutting saw. I use two laps, one for 

 rough grinding, the other for smoothing. I use No. 1. 

 emery and a little water with the first, and flour of emery 

 with plenty of water on the second. In preparing a speci- 

 men, I first grind a smooth surface on one side, and then 

 fix it to a plate of glass, of such a size as will suit my 

 specimen, with Canada balsam. I then reduce it in thickness 

 on the rough lap till I begin to see the light through it. 

 Then I begin with the smoothing lap, and reduce it with 

 flour of emery until every part of its structure is distinct. 

 If I choose to polish the specimen I do so on a lap made 

 of plush cloth or cotton vevet and putty-powder. I then 

 float them off the slide on which they have been ground, 

 and fix them on another with Canada balsam. I prefer, 

 where it is practicable, to mount them in balsam under a 

 thin cover in the usual way, as I am satisfied that the 

 structure is better brought out. 



In flint there are often found remains of sponges, shells, 

 Diatomaceae, &c. ; but to show these well, sections must be 

 cut and polished by the lathe and wheel of the lapidary, 

 which the microscopic student seldom possesses. Thin chip- 

 pings may, however, be made, which when steeped in turpen- 

 tine and mounted in balsam, will frequently show these 

 remains very well. 



Teeth are very interesting objects to all microscopists, 

 more especially to those who give much study to them ; as 

 the class of animal may very frequently be known from one 

 solitary remaining tooth. To examine them thoroughly, it 

 is necessary to cut sections of them ; but this is rather diffi- 

 cult to perform well, and needs some experience. Some 

 instructions, however, will at least lessen these difficulties, 

 and we will now endeavour to give them. 



Sections of teeth and bone may be successfully made by 

 rubbing slices cut with a saw between two plates of ground 

 glass, with water and a little powdered pumice-stone, the 

 old and partially worn glass being kept for the final 

 polishing of the sections. 



