374 CONNECTIVE TISSUES. 



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, Eanvier'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 milli- 

 metres 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. 



(6) Place in the following solution for twenty-four hours : 



Hydrokinone . . . . . 1 to 1-5 grm. 



Distilled water ..... 100 c.c. 



Formol . . . . . . 5 to 10 c.c. 



Rectified spirit . . . . 10 to 15 c.c. 



(7) Wash in water for some minutes. 



(8) Cut sections, and mount. 



The presence of nerve-end cells in the dental pulp was demon- 

 strated by MUMMERY (Phil. Trans. B., ccix, 1920), by means of a 

 modification of the gold method of Beckwith. 



Teeth, immediately after extraction, are placed in a solution of 

 formol and water or of formol and normal salt solution, preferably 

 4 per cent, of formol. This is, after a few days, changed to a 

 10 per cent, solution, and the teeth kept in this for at least a 

 fortnight. 



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

 formic acid in distilled water, to which 5 per cent, of formol may be 

 added. (Mummery states that neither he nor Dependorf has 

 ever procured good nerve preparations of teeth which have been 

 decalcified in the mineral acids.) 



Wash in running water for twenty-four hours, then for a few 

 minutes in distilled water. 



The pieces are taken from the distilled water and suspended by 

 threads in a large quantity of a weak solution of gold chloride 

 (1 in 5,000). Each piece should be suspended in at least 100 c.c. 



