270 THE AMERICAN MONTHLY [Deceuibcr, 



polished by the smooth glass, which is very desirable. The smoother 

 2:)ieces of glass when wet, allow the process of grinding to Ije watched 

 very closely and stopped at the right time. There is another advantage 

 in using two plates of ground glass, and that is, in the sides of the sec- 

 tion being ground quite parallel throughout the process. It is much 

 cleaner than the methods of grinding usually given in books on micro- 

 scopical manipulation, and is as applicable to woody shells of fruit and 

 teeth as it is to the osseous tissues. If sections of teeth with the en- 

 amel in situ are desired, a slight variation must be made from the method 

 just detailed. 



Hones of varying degrees of fmeness may be ol)tained at many tool 

 shops. The corundum, an imperfect form of ruby, having its hard- 

 ness but not its color, is ground fine, incorporated with melted shellac 

 and moulded into hones, hies, and wheels. Such a hone is a valuable 

 accessory in this process. Sections of teeth are difticult to make, on ac- 

 count of the excessive hardness of the enamel, a file making no percep- 

 tible impression on it if used dry, but if wet with water, a solution of soft 

 soap, or turpentine, it can be worked. But those who attempt to cut 

 it, even by these means, will find the saw, which is usually recom- 

 mended, but a poor tool against the enamel, and they will break many 

 saws before getting through it to the softer tissue beneath. A lapi- 

 dary's wheel is the only instrument with which numerous slices of a 

 tooth can be cut, the number being governed by the thickness of the 

 wheel ; but teeth can always be rubbed down on one side on a wetted 

 corundum hone, or, what is better, on a corundum wheel attached to 

 a lathe, if it is desired to make only one section. Having ground the 

 tooth down vertically to near its middle, it may be cemented with very 

 little heat to a piece of glass b}' using very old and hard Canada balsam, 

 and then the other side may be ground down. When ground to the 

 thickness of a card, it may be detached from the glass and further re- 

 duced to its final thinness between the plates of ground glass ; but this 

 method, while satishactory so far as the dental tissues are concerned, is 

 apt to leave the edges of the enamel chipped, frayed, and presenting 

 ragged edges. This may be obviated by grinding the section to the 

 middle as before, then polishing the surface very highly with a wet 

 hurt" leather charged with puttv powder. When this surface has re- 

 ceived the highest polish it is capable of taking, it may be cemented as 

 before with hard balsam, taking particular care not to heat the glass 

 slide to a greater degree than is sufficient to soften the balsam ; for if 

 made too hot, the polished surface of the section will be spoiled, pre- 

 senting somewhat the appearance of a china plate which has been 

 made too hot in the oven. Having attached the tooth firmly and in 

 closest contact with the slide, leaving a support of the balsam around 

 its edge, grind down the section to the utmost thinness and then highly 

 polish it, as with the previous surface. 



There will be, then, only a thin polished section needing to be 

 mounted, a proceeding which requires some care, if the work of hours 

 is to result successfully. Most of these hard tissues, whether of bone, 

 tooth, or nutshell, have an internal structure of great interest, whether 

 viewed with high or low powers. Thus in bone there are the lacunae, 

 with their exceedingly fine system of ramifications, in teeth the almost 

 similar lacunas of the cementum, the dentiiial tubuli, and the fibres of 



