26 PREPARING SECTIONS OF TEETH. 



operator, and when set withdraw the needle. Place it in a cool 

 place to harden. To prevent the object becoming displaced, it 

 should first be dipped in alcohol for some minutes in order to dry 

 the surface thoroughly. The sections are then cut with a razor 

 and kept flooded with alcohol, and the sections floated off the 

 knife into a capsule of the same. If desired, a mixture (by weight) 

 of white wax and olive oil, equal parts, melted together and poured 

 into the embedding dishes, may be used in place of the paraffin. 



To Embed in Gum.— If the tooth is in alcohol, transfer for six 

 hours into distilled water, then to a gum solution for six hours 

 (made of picked gum arable dissolved in water). Place a fair 

 quantity of the gum on the plate of the microtome (Cathcart's or 

 WiUiams'), and cool till nearly frozen. Place the tooth in position 

 and surround with gum, and let it freeze under a capsule, or by 

 means of the spray, till solid, but not brittle. The gum should 

 cut Hke cheese. When the sections are cut, transfer with a camel- 

 hair pencil from the knife to warm distilled water to dissolve out 

 the gum. From water transfer to spirit and spread the sections 

 out evenly. If the sections are delicate, they may be transferred 

 directly to the slide and treated with dilute spirit insitii. These 

 may be washed with water and stained with any agent or gold 

 chloride, and subsequently dehydrated and cleared and mounted 

 in any media. 



Decalcified Sections.— Picric Acid-- A saturated solution in 

 distilled water is the safest decalcifying agent, and it must be kept 

 saturated by the addition of fresh crystals every few days. When 

 soft enough^ prick with a needle to test it, and then wash well in 

 clean water to get rid of the acid and then in weak spirit, which 

 will dissolve more acid. Keep in pure alcohol and treat as 

 chromic acid for embedding, cutting, etc. Sections may be double 

 stained with picro-carmine and logwood, etc. 



Muller's Fluid.— This is one of the most useful hardening 

 agents we possess; it consists of bichromate of potash, 2 parts; 

 sulphate of soda, i part ; and water, 1 00 parts. Put the salts into 

 a pan with some of the water and boil till all is dissolved. Add 

 the rest of the water to cool it, and put in a stoppered bottle to 

 keep. After the first few days it does not require changing, but 

 requires longer time to harden according to the size of the tissue, 



