144 HISTOLOGY OF THE TEETH. 



the general way and direction of the enamel fibres, but to obtain 

 transverse sections exhibiting the fine striated appearance presented 

 when the axial portion is removed by acids, requires a shghtly dif- 

 ferent treatment. A method I have used with very fair success is 

 to choose as young a tooth as possible. Cut off the enamel by the 

 process previously described, and then grind one side (the inner 

 for choice) flat on an Arkansas stone moistened with water. Then 

 dry and mount on glass with old balsam, and very gently 

 rub down the opposite side. Great patience and care 

 must be used to avoid fracturing the specimen. To ensure 

 this, keep the tooth very moist. When thin enough, free 

 the section by soaking it in alcohol. Place it on a glass 

 slide, and then apply hydrochloric acid (i part in 15) on 

 a camel-hair brush. Leave for four or five minutes. Wash 

 the acid away with water, and examine under the microscope 

 to see if the axial portion is removed, and if not it must 

 again be treated with the acid. It should now be dried, and if 

 mounted in Canada balsam the gum should be nearly solid before 

 the section is introduced; but it is better mounted in glycerine jelly. 

 Dr. Abbott recommends that the enamel, after being sectionised 

 by the saw, should be carefully ground under water, and then 

 decalcified by immersing it in a dilute solution of chromic acid 

 for twenty-four hours. The solution is not to be stronger than 

 i per cent. Then stain with carmine, and mount in glycerine 

 diluted with half of its bulk of distilled water. 



Many other extremely useful stains might be mentioned, 

 amongst which are the anilin dyes and nitrate of silver. The 

 latter, however, should not be employed for staining dentine, but 

 I think what I have discussed at length will be found to meet all 

 ordinary requirements. 



Class II. — Softened Sections. 

 Several re-agents may be used. All seem to act by reiuoval of 

 calcareous matter and the hardening of the soft tissues of the 

 teeth. Chromic acid is the first. Half fill a pickle-bottle with 

 water ; then add chromic acid till the liquid is of a light straw 

 colour ; now tie a piece of cotton lightly round a fresh tooth and 

 suspend it in the fluid, so as to be well covered by the solution. 



