32 PREPARING SECTIONS OF TEETH. 



Staining with Chloride of Gold.— No other stain marks out so 

 clearly the minute anatomy of the soft tissues which penetrate 

 bone and dentine ; in fact, its excellence as a selective stain would 

 long ago have been demonstrated but for the recognised text-books 

 speaking of the great difficulty of using it and the length of time 

 it takes, and being only applicable to fresh tissues. 



True, fresh tissues always stain faster ; but teeth and bone, and 

 indeed other tissues, can be stained after having been severed from 

 the living body for a long time — sometimes weeks. Avoid the 

 use of metal instruments, bone, wood, or quill being preferable. 

 The use of steel does not, however, doom the staining to failure. 

 To stain (a) wash the sections in a solution of bicarbonate of soda. 

 (b) Put some i per cent, solution of gold chloride in a watch-glass, 

 test it with litmus paper, and, if acid, neutralise with {c) bicarbon- 

 ate of soda by drops. Place the sections in the solution and 

 cover the watch-glass with a lid to keep it in total darkness for from 

 half to one hour until the sections are straw-colour. 



Remove the sections from the staining fluid to distilled water, 

 leave covered over for a few minutes (they must not be exposed to 

 the hght for more than a few seconds), {d) Put some i per cent, 

 formic acid in a watch-glass, float the glass on hot water, put the 

 sections in the acid, cover them over and keep them in the dark 

 and fairly hot until they turn crimson, which will be in about an 

 hour, {e) When stained, immerse the sections in cold distilled 

 water for about half-an-hour. (/) Dry the sections and mount 

 them in glycerine jelly; avoid Canada balsam. Keep gold chloride 



bottle in the dark. 



Sections to show pulp (particularly hyperaemia) are difficult to 

 make and to retain the natural injection. First, Catch your hare — 

 i.e., capture the condition — examine a suitable case when one is 

 presented, note condition of the tooth itself, etc. Remember tke 

 condition of the tooth at the moment of extraction^ especially as to 

 pain, as it is of vast importance in studying this object. Extract 

 this tooth ; place in Muller ; do not handle or disturb in any way 

 for a week at least, Then harden ; wrap the tooth in muslin and 

 place in the jaws of a powerful vice (not one where the jaws are 

 so weak that they will spring together on cracking the tooth, as it 

 will crush the pulp), and steadily close them until the tooth cracks 



