PREPARING SECTIONS OF TEETH. 33 



open. If skilfully done, the line of fracture will be the long axis. 

 Then place in Muller's fluid, freshly filtered, and carefully lift the 

 pulp from its cavity. (Carefully do this, for the dentinal fibrils 

 will be pulled out a considerable length.) Now place in a thin 

 solution of gum arabic, to which should be added some gum 

 camphor, salicylic, thymol, or carbolic acid, to prevent mould. /;/ 

 no case fmist this gum be sfro?ig enough to float the pulp. If of 

 greater specific gravity than the pulp the tissue shrinks. Evapo- 

 rate the gum arabic solution slowly to the consistence of a thick 

 jelly. This should require three or four days to thoroughly pene- 

 trate the pulp. When the solution is hard enough to handle, the 

 pulp is taken up with some mucilage, placed in the position for 

 cutting on a piece of cork afloat on alcohol, with the pulp side 

 down. In from twelve to thirty-six hours the surface will be con- 

 siderably hardened by the abstraction of the water by alcohol. 

 Do not let it get too hard. Insert in a microtome ; use paraffin 

 or some suitable substance for embedding, and allow to stand 

 twelve to twenty-four hours. Several sections can be cut if desired, 

 the specimen being kept wet in alcohol all the time. Mount 

 direct in glycerine without dissolving the mucilage, or dissolve it 

 out in tepid distilled water, stain the pulp with haematoxylin or 

 fuchsin, and mount in Canada balsam. 



If a tooth is extracted during a paroxysm of pain, inflamma- 

 tion of the pulp is almost uniformly accompanied by the signs of 

 hyperaemia, they being present in a marked degree in the imme- 

 diate neighbourhood of the inflammatory area; but if the tooth is 

 extracted during a period of quiet, the hypersemia is limited to the 

 vessels within the inflamed area. 



Celloidin.— After well hardening, place for twenty-four hours in 



equal parts of ether and alcohol, transferring to a syrupy solution 



of celloidin, made by dissolving celloidin in a mixture of equal 



parts of alcohol and ether. Leave it for about twenty-four hours ; 



cover the object with a thicker solution of celloidin, and allow it 



to remain in it for twenty-four hours. When ready, embed on cork. 



Spread on the cork a little of the celloidin solution and allow to 



dry ; then another coat and let dry. Now place on it the specimen 



as quickly as possible before the celloidin begins to harden. Then 



cover the whole with successive layers of the celloidin solution 



International Journal of Microscopy and Natural Science. 

 Third Series. Vol. III. d 



