HISTOLOGY OF THE TEETH. 149 



the evaporation of the alcohol and ether. When the mass is 

 sufficiently hardened — which will require a longer or a shorter 

 time, according to the size of the mass — place in a mixture of 

 equal parts of alcohol and water to harden ; then remove from the 

 paper box. Cut sections with a flat razor, dipped in methylated 

 spirit or equal parts of alcohol and water, float sections off on 

 the same fluid. Strong alcohol must not be used, as it 

 softens the mass. The sections may be kept in a bottle filled 

 with equal parts of alcohol and water until required for use. 

 Having cut our sections, we are ready to stain and mount them. 



If it is desired to mount in balsam and benzole — which I 

 consider the best for permanent tooth preparations — either one 

 of two methods may be used. First, the dehydrated stained 

 specimen may be placed in a dish containing oil of cloves, and 

 the celloidin removed, after which they may be mounted in the 

 usual manner. Second, the unstained sections may be placed on 

 the slide, on which there has previously been dropped a suffi- 

 cient quantity of oil of cloves to fix, but not to float the section, 

 after which it may be stained on the slide, dehydrated, and 

 mounted in the usual way. The latter is especially applicable to 

 very large, thin sections, as it obviates the necessity of re-handling. 

 I believe that embryonal tissues do not permit of very elaborate 

 and complicated staining methods. The brilliancy of the result 

 depends on a combination of different tissues with their different 

 chemical reactions. These are found only in matured tissues, 

 especially in the lower order of animals. The best results I ever 

 saw were some sections of the head of the newt and common 

 snake. 



To show teeth, only four stains are requisite, viz. — haema- 

 toxylin or logwood, eosin, picro-carmine, and methyl-green, 

 valuable in the order named ; or as double -stains in combinations 

 of hsematoxylin and eosin, haematoxylin and picro-carmine, eosin 

 and methyl-green, and picro-carmine and methyl-green. Double- 

 stains give the best results. Tissues that have been hardened in 

 chromic acid require to be placed in a i per cent, solution of 

 carbonate of soda from fifteen to twenty minutes to remove the 

 chromic acid. 



To double-stain sections thus prepared with haematoxylin 



