34 PREPARING SECTIONS OF TEETH. 



until the object is built up quite firm. When it has dried remove 

 the celloidin from the glass with a sharp knife, and if necessary 

 trim the mass to a proper size and form. 



To place on Cork.— Coat the cork with celloidin solution and 

 let it dry (to prevent air rising from the cork), The object is now 

 placed in its hardened matrix and mixing cell, as on the cork, by 

 means of celloidin. Let dry in air till it retains its shape well. 

 Drop the cork into 50 per cent, alcohol, and it can usually be cut 

 after soaking it for one hour. For dental embryological work it is 

 excellent. 



Developing Teeth Sections.— Take the teeth that are forming 

 in the jaws of embryos, at or nearly the time of birth, while the 

 tissue is still warm if possible. Place in ^ to J of i per cent, 

 solution of chromic acid and change daily for three or four days. 

 The edges of the dentine that were calcified are found sufficiently 

 softened to make a number of sections. Take the teeth from the 

 acid solution, wash in distilled water, and then place in a solution 

 of gum arable for several hours. Then put in alchohol to take 

 out the water. Paraffin and wax are melted and poured into a 

 convenient mould. When clouded with cooling, embed the tissue, 

 and cut it until the calcified tissue is reached. Place the sections 

 in distilled water for a few minutes to dissolve out the gum, and 

 then put in glycerine and alcohol and mount in glycerine. 



For further details on Embryonic Teeth Sections, see paper on 

 Histology of the Teeth in this Journal, New Series, Vol. 11. , 1889, 

 where they are given at length. 



Preparing Sections of Decayed Dentine.— Select a freshly- 

 extracted decayed tooth, wash out all the particles of food, and 

 break away the margins of enamel so as to expose the softened 

 dentine as much as possible. Then with a sharp instrument cut 

 away the decayed portion from the sound dentine, keeping the 

 instrument well to the latter, and we thus get a large piece of 

 decayed dentine. Immediately freeze the tissue in gum, stain and 

 mount. 



Staining Tissues. — This requires a little practice to secure good 

 results, so we will take the simplest — namely, logwood. Buy a 

 good sample, or make one from the many receipts found in all 



