210 THE MICROSCOPE. 



in the fangs, to exhibit the anastomoses of their branches. 

 The dental cartilage is easily shown by maceration in 

 hydrochloric-acid, a process which requires a longer or 

 shorter time, according to the concentration of the acid. 

 It is very instructive also to macerate thin sections in 

 acid, and to examine them upon a slip of glass, at 

 intervals, until they entirely break up. The enamel 

 prisms are readily isolated in developing enamel in this 

 way, and the transverse lines readily seen when the section 

 is moistened with hydrochloric acid. The early develop- 

 ment may be studied in embryos of two, three, or four 

 months with the simple microscope ; and in transverse 

 sections of parts hardened in spirits of wine. The pulp of 

 mature teeth is obtained by breaking them in a vice, and 

 the nerves can be made out without difficulty on the addi- 

 tion of a dilute solution of caustic soda. 



To cut through the enamel of the tooth, it will be 

 necessary to lessen the friction, by dropping water upon 

 the saw as it is made to revolve. The section is after- 

 wards very quickly ground down by holding it against 

 the flat side of the corundum-wheel.^ A small handle, 

 mounted with shell-lac, to fix the section in, forms a readv 

 liolder : polish, as before directed, between two pieces of 

 the water-of-Ayr stone, or on a hone of Turkey-stone kept 

 wet with water. As the flatness of the polished surface is 

 a matter of the first importance, that of the stones them- 

 selves should be tested from time to time ; and whenever 

 they are found to have been rubbed down on one part 

 more than another, they should be flattened on a paving 

 stone with fine sand, or on a lead plate with emery. When 

 this has been sufficiently accomplished, the section is to be 

 secured, with Canada balsam, to a slip of thick well- 

 annealed glass, in the following manner : — Some Canada 

 balsam, previously rendered somewhat stiff by evaporation 

 of part of its turpentine, is to be melted on the glass-slip, 

 so as to form a thick drop, covering a space somewhat 

 larger than the size of the section, and it should then be 

 set aside to cool ; during which process, the bubbles that 

 may have formed in it will usually burst. When cold, its 



(1) Corundum is a species of emery composition ; alumina, red oxide of iron, 

 and lime; it is much used by dentists as a polishing material. 



