28 PREPARING SECTIONS OF TEETH. 



Osmic acid, i per cent., shows the contours of the constituent 

 tissues, the nerve-fibres being more especially distinct. Again, 

 both fresh and chromic acid specimens may be treated with osmic 

 acid. Carmine is, perhaps, the best stain for pulps. 



To examine the pulp together with the enclosing dentine, the 

 specimen is softened in chromic acid and then embedded in cel- 

 loidin, or paraffin, or wax, as above described. The fresh pulps 

 of lower incisors are the thinnest and best adapted for examining 

 the system of blood vessels, and if transferred to the sUde when 

 fresh, add some normal saline solution, cover, and with careful 

 pressure the pulps may be spread and examined. 



The Blood-Vessels of the Pulp, To Study.— Chloroform an 

 animal, and just before respiration ceases open the right auricle 

 and let the vessels empty themselves ; then inject with Prussian 

 blue, warmed to a temperature of 40^ C. to render the gelatine 

 fluid, and also to prevent any vascular spasm which a cold fluid is 

 very liable to produce. Then place the head in alcohol for 

 twenty-four hours to harden the injection ; or, if preferred, in 

 Muller's fluid or chromic acid, which is quite as good and in my 

 opinion better. The pulp, after hardening in alcohol, is removed 

 and immersed in a weak solution of chromic acid, and at the end 

 of ten days sections of it may readily be cut and then mounted in 

 glycerine jelly. If the animal is quite dead, you must wait till 

 rigor mortis has passed off and inject a non-gelatinous Prussian 

 blue, but the first injection is the best. In animals which die of 

 strangulation the vessels will be found so gorged with blood as to 

 render any further preparation unnecessary. 



If the tissues are partially decalcified in a very weak solution 

 of chromic acid and treated as above described, sections can be 

 frozen, cut, stained, and mounted, so as to show the dentinal 

 fibrillae as prolongations of the odontoblasts. 



I prefer to harden teeth well in Muller's fluid, then spirit, and 

 then to grind sections, keeping them wet all the time, and if wished 

 they can, after grinding, be embedded in celloidin and decalcified 

 in half per cent, solution of chromic acid, then treated and 

 stained as desired. A point worthy of remembrance is the dis- 

 similarity between caries of bone and decay of teeth, as the reac- 

 tion is totally different when they are treated with picro-carmine. 



