PREPARING SECTIONS OF TEETH. 29 



Perenyi's Fluid.— As yet I have had very little chance to 

 thoroughly test this agent, to which Dr. N. S. Hoff, of the Uni- 

 versity of Michigan, very kindly drew my attention, but it promises 

 to be a good agent, having the properties of hardening and decal- 

 cifying at the same time. The formula is : — Nitric acid (lo per 

 cent.), 4 parts ; alcohol, 3 parts ; and chromic acid (o'5 per cent.), 

 3 parts. Mix. Leave the tooth in this agent some four hours or 

 more, until soft. The softening is facilitated if the tooth can be 

 cut through at the neck so that the agent can enter the canal. 

 Then transfer to 70 per cent, alcohol for twenty-four hours, strong 

 alcohol for some days, absolute alcohol four or five days. For 

 ordinary tissues combine the stain with the fixing fluid. Fuchsin 

 may be dissolved directly in the fixing solution. But eosin, pur- 

 purin, or aniline violet must first be dissolved in three parts of 

 alcohol, and then shaken into the liquid. 



Picro-carmine and borax-carmine can also be added, but as a 

 precipitate results it must be filtered, and after staining pass 

 through 50 per cent, alcohol for five hours ; ordinary spirit, ten 

 hours, and then into absolute alcohol. If the tissue is unstained, 

 it may, after cutting, be immersed in clove oil coloured with an 

 alcoholic solution of eosin or sapranin, or it may be placed on the 

 slide for five to ten minutes, with a few drops of the coloured oil. 



Kleinenberg's fluid is also useful for decalcifying teeth. 



To Clean Cover-Glasses.— Take the cover-glasses from the wool 

 in which they are usually kept, and place them in a beaker, cover 

 with strong sulphuric acid ; stir, to get rid of all the air remaining 

 amongst them and leave them for an hour or two. Then wash 

 well in several changes of water to get rid of the acid, and place 

 in alcohol, from which they are taken one by one, and wiped dry 

 on an old handkerchief, and then polished with a chamois leather 

 and kept for use in an air-tight box. 



Retaining the Soft Parts of Bone and Teeth.— Take a fresh, or 

 nearly fresh, tooth. Divide it at once with a sharp fretsaw below 

 the neck into two or three pieces, " allowing distilled water to 

 trickle over it the while," and then the reagents and stains can 

 penetrate the pulp cavity. Place the pieces in concentrated sub- 

 limate solution for some hours to fix the soft parts. Wash in 

 running water for about one hour ; then place for twelve hours in 



