HISTOLOGY OF THE TEETH. 147 



Stain the sections in carmine, and then mount in Canada balsam to 

 render them translucent. Picro-carmine is an excellent stain. If 

 they are not stained, they will be opaque from chromic acid and 

 alcohol. To render them transparent, allow them to soak in oil of 

 cloves. As most tooth-germs are taken from newly-born kittens 

 and puppies, chromic acid maceration must be much longer and 

 may be even extended to a couple of months ; but the period 

 may be shortened by the judicious use of an occasional few drops 

 of nitric acid. 



There are a great many hardening fluids ; but a i per cent, 

 solution of chromic acid is the best for our use, or 15 grs. of 

 chromic acid and 2 cc. nitric acid, and 200 cc. water (Rutherford). 

 Add the nitric acid last. If the softening is not completed in a 

 month, place double the quantity of nitric acid in the fluid, or 

 place them simply in dilute nitric acid (2 per cent.). 



Staining in Carmine, Hsematoxylin, etc.— Teeth may be 

 mounted dry by grinding both sides down on an oil stone very 

 thin; then polish on soft leather and finely-powdered pumice-stone. 

 Mount in Canada balsam and benzole which has been heated, 

 and then allowed to get ?iea?iy solid. Press the section down 

 firmly, and then apply the cover-glass. In this way air-bubbles 

 rarely get under the section. 



Chromic Acid (i per cent.) decalcifies as well as hardens. 

 This is made by adding 30 grs. of acid to a quart of water. 

 The tissue (as fresh as possible) should be put into the solution, 

 and the fluid changed every other day for one week, and then left 

 until completely decalcified. Then place them in 75 per cent, 

 alcohol to remove the chromic acid. Tissues can be prepared in 

 this way in any quantity, and kept in alcohol until needed. This 

 is the usual method. For the demonstration of the develop i/ient of 

 teeth, I have used the ja\vs of fcetal kittens, dogs, rats, rabbits, 

 and also sections of fully-developed teeth and sections con- 

 taining the teeth in situ. Mr. Hunter (of Sands and Hunter, 

 Cranbourne St.), London, has some fine preparations of the 

 whole jaws, etc. Young foetal pigs are also readily obtained in 

 good condition. A series of these should be secured, ranging in 

 length from one inch to six inches, the first presenting the begin- 



