HISTOLOGY OF THE TEETH. 141 



solution for a few minutes, and then transfer to a i per cent, 

 solution of formic acid. Keep warm over a water-bath for about 

 an hour and a half, and mount in glycerine jelly, not Canada 

 balsam. Sections which have been decalcified by chromic acid 

 take longer to stain than those which are fresh ; but the whole 

 process only occupies from three to four hours, instead of at least 

 twenty-four hours, as in the old method, and the result is far more 

 satisfactory. The usual needles, or any steel instruments, must be 

 replaced by non-metallic ones^ such as a glass rod or quill tooth- 

 pick, etc., for manipulating the sections. 



x\ better way to classify dental microscopy is to divide it into 

 treatment demanded by — (i) Hard Sections, (2; Softened Sections, 

 (3) Sections of Pulp, (4) Sections of Tooth-Germs, etc. 



Class I. — Hard Sections. 



Choose your tooth, the fresher the better. You will find, with 

 care, that two or three sections may be cut from a tooth by using 

 a new, thin, gold file to cut through the enamel, wet with tur- 

 pentine and soft soap, and then use a broad-frame saw for 

 cutting through the dentine. The best way is to hold a section of 

 tooth about one-eighth of an inch in thickness. You next flatten 

 one side on a fine revolving corundum wheel (Ash's No. 9, fine), 

 till one side is ground quite flat. Then polish that side to the 

 most perfect polish it is capable of receiving on a piece of wet 

 buff leather, with some putty powder on it. Afterwards take a 

 piece of stout plate-glass, about 2 inches square. Put a little old 

 and consequently tough- Canada balsam on it, warm, and spread it 

 a little larger than your section. Let the balsam cool down till it 

 is " tacky " ; then press the polished side of the tooth into close 

 contact with the glass. When quite cold, the grinding may 

 proceed, as in the first part of the operation, till you get the 

 required thinness, when the side may also be polished. The hard 

 balsam round the section supports and protects the edges, which 

 will not be fractured (unless heated too much) and made jagged 

 and untidy. In 7iot putting the tooth on to glass till the balsam is 

 somewhat cool, you prevent the polished surface from being 

 covered by fine cracks, and also the balsam from running into the 

 tubular structure of the dentine. 



