HISTOLOGY OF THE TEETH. 145 



Change the solution every two or three days, and it may be 

 gradually strengthened till of a pale sherry colour. At the end of a 

 week one or two drops of hydrochloric acid is to be added. When 

 decalcified (test with needle), embed, and cut with a razor. Dip 

 the tooth first in melted paraftin, and place it nearer the side next 

 the operator, so that it comes quickly in contact with the knife. 

 The " Army " razor is best, as it can be flooded with methylated 

 spirit, and the sections floated off the knife into alcohol. To 

 prevent the object from becoming displaced, it should be first 

 immersed in alcohol for some minutes in order to dry the surface 

 thoroughly. 



To Embed in Gum.— If the tooth is in alcohol, transfer for six 

 hours into distilled water, and then to a gum solution for six hours. 

 Place a fair quantity of gum on the plate (Cathcart's microtome), 

 and cool till nearly frozen. Place the tooth in position, and continue 

 the spray till the gum is solid, when it will cut like cheese. No 

 previous wetting is necessary, as the thawing of the ice keeps the 

 knife moist. Place the sections in weak methylated spirit. If the 

 sections are delicate and liable to break, transfer them from the 

 knife to the slide, and treat them /// situ with dilute spirit. These 

 sections may be stained with carmine or gold chloride, and then 

 mounted either in glycerine jelly or Canada balsam. A saturated 

 solution of picric acid is preferable to chromic acid, as it causes 

 less shrivelling than the latter. A less good one is a saturated 

 solution of alum, with the addition of ^y drachm of hydrochloric 

 acid to I ounce of the alum solution. Dr. L. Beale softens the 

 tooth by a prolonged maceration in glycerine, to which a few 

 drops of acetic acid may be added to hasten the process. 



Class III. — Sections of Pulp. 



Crush newly-extracted teeth in a vice or with a hammer, and 

 select several pieces of dentine with portions of pulp adhering to 

 them. Then immerse them in carmine fluid, cover with paper, 

 and leave in a warm place for a couple of days. Then pour the 

 fluid off, and wash the specimens in a solution made of strong 

 glycerine 2 parts, distilled water i part, and leave for a couple of 

 hours to soak. To enable the tissues to regain their original 



