140 HISTOLOGY OF THE TEETH. 



enamel, may be studied in the much more advanced incisors, 

 which, as just pointed out, extend backwards in these animals 

 through the greater part of the length of the jaw. 



Sections skewing the Pulp.— As soon as the tooth is 

 extracted, immerse it in alcohol till required for use. You 

 will now require a lathe with emery wheels of 5 inches 

 diameter and | of an inch thick, also a small felt wheel 

 for a pad to hold the section whilst cutting. Hold the spe- 

 cimen to the circumference of the wheel with the thumb and 

 finger of each hand. Cut down the tooth on each side until the 

 pulp is seen, sliding the tooth backwards and forwards across the 

 wheel in order to grind evenly from the crown to the apex of the 

 root. Keep the wheel wet with distilled water. Now return the 

 tooth to alcohol, and keep it there for a short time (half-an-hour). 

 When again grinding, use the flat surface of the same wheel, 

 cutting first one side and then the other, until the section is about 

 one-eighth of an inch thick. Now use the finer wheel, and go 

 from that to the finest for the last polishing, returning the section 

 occasionally to alcohol for a few minutes in order to keep the pulp 

 as hard as possible. Use the felt wheel as a bed for the section 

 while grinding. Cut the tooth on each side alternately to insure 

 taking the section from the centre of tooth. When thin enough, 

 wash carefully in distilled water, and examine under i-inch object- 

 glass, to see that all the felt wheel fibres are washed from the 

 pulp. Now stain the pulp with carmine, and keep the section in 

 alcohol until ready to mount, when it should be immersed in 

 clove oil, and then in thin balsam. 



To demonstrate Protoplasm between the Fibres of the 



Enamel.— Decalcify teeth by means of chromic acid. Then cut 

 sections, and stain in a solution of gold chloride, exposing to 

 sunlight for twenty-four hours or more. Gold chloride is said only to 

 stain when fresh. But I think, if examined and more carefully 

 manipulated, this does not matter. I immerse my sections, 

 either cut from a decalcified tooth or ground down from a hard one, 

 in a solution of carbonate of soda for an hour. Then place in a 

 solution of chloride of gold, which must be neutral. Leave in the 

 dark for another hour. Again place in the carbonate of soda 



