138 HISTOLOGY OF THE TEETH. 



The Pulp of a full-grown tooth can only be investigated by 

 breaking the tooth across with a hammer. The broken tooth 

 should then be hardened for twenty-four hours in a one-fifth per 

 cent, solution of osmic acid. 



Break a fresh tooth, and place it in a saturated solution of 

 picric acid. Add more crystals of the acid occasionally and stir until 

 the tooth becomes soft, when transfer to alcohol. Change the 

 spirit so long as it becomes tinged with the picric acid. This will 

 preserve the pulp and odontoblasts. Sections can be now cut, 

 stained with carmine (which double stains), logwood, etc., and 

 mounted in glycerine or Farrant. 



The Dentinal Sheaths lining the tubules may be isolated 

 by boiUng for ten minutes in strong sulphuric acid (i per cent.). 



The Tubules appear to be calcified membranes, imbedded in 

 a calcified tissue somewhat similar to that of bone. The latter 

 disappears when boiled in the dilute acid. 



The Odontoblasts and Fibres of Tomes may be seen in 

 sections of the teeth m situ^ when they are very young and still 

 within the dental sacs. 



Carious Teeth.— Break them, and make sections from the 

 portions which have become brown and deprived of their lime 

 salts. But if one desires to follow the transition from healthy to 

 diseased tissue more closely, the previous decalcification is good. 

 Tingeing with carmine and iodine also renders good service. 



Exner's Method.— Drop melted wax on the end of a cork until 

 the tooth can be fastened in it. Then add more wax until the 

 tooth is completely covered. Grind wax and tooth very carefully 

 on an ordinary grinding stone w^hich is turned with a handle. 

 When a smooth surface has been obtained, soften the wax and 

 remove the tooth. Embed it a second time with the ground 

 surface downwards, and grind as before, until the wax can be seen 

 through the tooth substance. Then finish with pumice-stone and 

 a hone as for sections of bone. 



Dentinal Sheaths.— To show these lining the tubules, a piece 

 of softened \.QQ\h (lo per cent, hydrochloric acid) is transferred to 

 strong hydrochloric acid (contained in a watch-glass, which is 

 covered by another, inverted). Leave in this for an hour, after 



