181 
that will turn bones yellow. Carbon tetrachloride has none of these 
faults and is safer and preferable for other reasons. It is a colourless 
compound, only slightly poisonous, and is very heavy, so that grease 
floats to the surface. If the solutions become dirty, they may be skimmed, 
filtered, and used again. 
Treatment of Teeth 
The teeth of large skulls, particularly those of bears, wolves, deer, 
etc., have an annoying tendency to crack. This is usually due to sudden 
changes of temperature, which cause the enamel to shrink or expand at 
a different rate from that of the bony centre of the tooth. Therefore, the 
skulls should not be suddenly changed from hot to cold water. The 
cracking of teeth may be diminished to some extent by coating them with 
melted paraffin, but this method is not very dependable. A much better 
method is to coat each tooth with a thin solution of Ambroid cement, 
thinned down with Ambroid solvent or acetone. This forms a very thin 
elastic film on the tooth and prevents it from cracking, or if the tooth is 
already cracked, holds the pieces together. If the Ambroid cement is put 
on too thickly, it discolours the tooth slightly, but it may be dissolved and 
sponged away with acetone at any time. 
A more recent and better method described by Mr. A. Lucas (1924) 
consists of using celluloid dissolved in acetone. Merely by varying the 
proportion of acetone in which the celluloid is dissolved the solution may 
be used for coating teeth, for impregnating porous materials that are in 
need of strengthening, as a waterproof, air-tight varnish, or as a strong 
but semi-flexible cement. It is prepared by cutting colourless sheet cellu- 
loid into small pieces and dissolving them in a bottle of acetone. If it 
becomes too thick it should be thinned with acetone; if it is desired as a 
cement, it may be allowed to evaporate for a few minutes in a shallow 
dish, w'hen the viscosity will increase rapidly (Leechman, 1931, 131-2). 
Teeth, particularly the milk teeth of young animals, frequently drop 
out in the cleaning process, and care should be taken not to lose any. The 
ordinary method of setting loose teeth is to dabble a wisp of cotton in 
liquid glue and wrap it around the root of the tooth before putting the 
tooth back in the socket. A better method is to force a small pellet of 
plasticine into the tooth socket. This will hold the tooth effectively and 
permit its removal for examination at any time without danger of crack- 
ing the alveoli of the jawbone. 
After the skull is cleaned and bleached, the cranium and lower jaws 
each have the catalogue number and sex neatly marked on the bone in 
black carbon ink. Skulls are frequently laid out in series for study and 
if not plainly marked are apt to become mixed. Small skulls are most 
conveniently kept in cylindrical glass vials of appropriate size (2 inches 
depth, and diameter varying from \ inch to 1 inch). Larger skulls may 
be kept in pasteboard boxes. Large skulls should have the jaws separated 
by a bunch of crumpled paper to avoid chipping of the teeth. 
Whether small skulls are kept in the same storage case as the skins 
to which they belong is a matter of individual preferences or circumstances. 
Skulls are apt to rattle about when trays are taken out, and in practice 
skulls and skins are usually compared separately. However, it is often 
convenient to keep them together, making if easy to take out individual 
