202 ON THE PREPARATION OF TOOTH SECTIONS. 



withdrawing it, the alcohol evaporates, leaving the porous structure 

 completely occluded and protected from the balsam, however 

 liquid it might be. I think that both these methods are produc- 

 tive of such satisfactory results that I can commend them to your 

 careful attention if you should at any time wish to preserve speci- 

 mens of dental histology. 



The methods of preparing sections of teeth by decalcification, 

 though not new, have come in vogue of late. Many specimens 

 are better prepared by softening the hard parts, and cutting, after 

 suitable preparation, in a microtome. There is no doubt that 

 decalcifying processes are most useful in many instances. Chromic 

 Acid has for years been used for this latter purpose. It is claimed 

 for it that it hardens the soft parts while it softens the hard, both 

 changes taking place simultaneously. It is useful for fully- 

 developed human teeth, also for developing jaws of mammals in 

 which a fair amount of dentine, enamel, and bone, have been 

 already formed. The following is, though seemingly rather com- 

 plicated, wasteful, and troublesome, a very successful method : — 



I. — A tooth is placed in a solution of Chromic Acid (crystals), 

 lo grains, to Water, 8 ounces. It should here remain for two days, 

 at the end of which a fresh solution must be used. 



2. — After two days immerse it in a solution of Chromic Acid, 

 2o grains, to Water, 8 ounces, for four days. 



■ 3. — Then in Chromic Acid, 2 ounces ; Water, 4 ounces ; 

 Hydrochloric Acid (2% solution), 4 ounces. The latter should be 

 added a few minutes after the Chromic Acid solution is made. 



4. — Remove the tooth to fresh solutions, made up according 

 to the last formula, every fourth day until it is sufficiently soft (this 

 takes from eleven to twelve days). By using the Chromic Acid 

 as mentioned, the advantages derived from the employment of 

 fresh re-agents are assured. 



5. — Immerse the tooth for half-an-hour in a large quantity of 

 alkaline solution, and wash under the tap for twenty-four hours. 



The tissue is then ready for gum solution and cutting with the 

 microtome. Embedding in paraffin may of course be substituted 

 for the gum. Picric acid, in a saturated solution, is often employed 

 for the purpose of decalcifying. But for a ready solution that is 

 generally to hand, and the method I myself employ, there is 



