430 BONE, TEETH 



formol, decalcifies in 10 per cent, nitric acid (eight to fourteen 

 days, change frequently) and makes celloidin sections. 



For decalcification of teeth, see also § 589 (Rousseau, Bodecker 

 and Fleischmann), Bddecker finds Rousseau's process not 

 applicable to human teeth : the acid must be added to the fluid 

 celloidin. 



For the study of the lymphatics in the dental pulp, Dewey and 

 NoYES {Dental Cosmos, lix, 1917, pp. 436 — 44) first inject the 

 blood-vessels with carmin -gelatin. Then 2 grm. of Prussian 

 blue (oil colour in tubes) is stirred with 3 grm. of turpentine 

 oil in a glass mortar for five minutes ; 15 grm. of sulphuric ether 

 is added, and this fluid filtered through flannel or chamois skin. 

 After the injection of this fluid the head is placed for twenty- 

 four hours or longer in 20 per cent, formalin, and then the injected 

 teeth are carefully removed and the pulps examined. Later it 

 was found that more constant results were obtained when the 

 injection of the blood-vessels followed that of the Prussian blue. 

 Prussian blue injected directly into the pulps and trypan blue or 

 lithium carmine injected intravenously or intraperitoneally were 

 also employed. See §§ 515-553. 



Wellings {Proc. Sixth Internal. Dent. Cong., pp. 47 et seq.) 

 demonstrated intra-vitam staining of dental and adjacent tissues 

 by means of trypan blue (§ 748). 



Mummery {Phil. Trans. B., ccii, 1912), for the fixation of the 

 nerve-tissue of the dental pulp, finds formalin to be preferable to 

 all other fixing agents, employing 10 parts of the 40 per cent, 

 commercial formalin to 90 parts of water. 



Decalcification is effected by means of 33-3 per cent, formic 

 acid. After thorough washing he leaves for twenty-four hours 

 in a strong solution of dextrin (which he finds preferable to gum 

 arabic), and sections are cut on the freezing microtome, by the 

 employment of which he is able usually to obtain thinner sections 

 than when paraffin is used for imbedding. 



The sections are stained either by means of iron and tannin, 

 iron hsematoxylin (Benda), Congo red, Ranvier's modification 

 of Lowet's gold chloride process, or by Cajal's method, 

 where : — 



1. Small pieces of the decalcified tooth, not more than 4 mm. 

 thick, are placed in 50 c.c. of rectified spirit, to which 3 or 4 drops 

 of ammonia may be added, and kept in this solution for from 

 four to six hours. 



2. Transfer to absolute alcohol for twenty-four hours. 



3. Rinse with distilled water. 



4. Place in a large quantity of 1-5 per cent, solution of silver 

 nitrate, and keep in warm incubator at about 35° C. for five or 

 six days, 



5. Rinse in distilled water for a few seconds. 



