428 BONE, TEETH 



decalcification process, 1 to 2 c.c. of HCl are added daily until the 

 bones become flexible ; they are then washed out for a few days 

 in a saturated solution of sodium chloride. The solution soon 

 becomes acid, but is continuously neutralised by the addition of 

 traces of dilute ammonia. Rinsing out continues until the bones 

 cease to lose acid. 



Ebner's fluid acts very slowly, but gives good results. The 

 thin well-washed sections are stained in gentian violet and 

 differentiated with anilin oil and xylol (2 : 3). This process 

 ensures the staining of the ground substance, fibrillae of Ebner, 

 and the Sharpey fibres. 



914. Decalcification of Bones and Teeth, see Chapter XXVI., 

 pp. 250-253. 



915. Sections of Bones or Teeth showing the Soft Parts. A 

 developing tooth with its epithelial enamel-organ, its mesodermal 

 dentinal papilla, and its layers of partially calcified enamel and 

 dentine, is made up of very delicate structures of different con- 

 sistency and so is peculiarly liable to unequal shrinkage, with con- 

 sequent distortion during the period of fixation and in the sub- 

 sequent processes passed through in the preparation of sections. 

 Further, post-mortem changes in the ameloblasts occur within a 

 very few minutes after death, leading to a less precise behaviour 

 to stains than is found in the case of cells which are fixed 

 immediately after death. 



For the examination of developing teeth in situ, jaws may be 

 fixed in corrosive-formalin-acetic mixture, in Bouin's picro- 

 formol, in Zenker's mixture or Helly's modification thereof, or in 

 Sansom's modification of Carnoy's mixture (§ 90). 



For the study of the micro-anatomy of the enamel-organ and 

 the dentinal papilla, a young pup or a kitten, two or three days 

 old, is killed, preferably by a blow on the head. The jaws are 

 removed and the bone of the under-surface of the mandible 

 pared away by a sharp scalpel until the bases of the tooth-germs 

 are almost exposed. The muco-periosteum is grasped with a 

 pair of forceps and stripped from the bone, when the tooth- 

 germs will come away attached thereto. 



Sansom's modification of Carnoy's mixture, employed at blood- 

 heat, is particularly effective when the tooth-germs have been 

 exposed in the manner outlined above, fixation therein being 

 complete in from five to ten minutes. They are then passed 

 through successive baths of alcohol of 30 per cent, and 50 per 

 cent., each for fifteen minutes ; 70 per cent., to which is added 

 tincture of iodine, for four hours ; 90 per cent, for thirty minutes ; 

 and into two changes of absolute alcohol, each for fifteen minutes 

 or longer. 



The tooth-germs are then transferred to a mixture of equal 

 parts of absolute alcohol and carbon disulphide for one hour, 



