638 ON THE DISEASES OF THE TEETH OF THE HORSE. 
and guarded on the sides by two circular shields, which, when 
used, will entirely prevent its displacement. This is intended 
to be used principally for the back or posterior teeth, the angle 
formed by the upper and lower jaw becoming less, as you are 
aware, towards the back of the mouth, and consequently any 
instrument requiring more space could not be so well applied. 
In some instances, where necrosis has taken place, and the 
forceps cannot be used, and the tooth is sufficient^ loose to 
allow you, with such an amount of traction as can be made by 
the aid of this instrument it may be displaced. This may also be 
applied, with the guarded chisel, for the reducing or chipping 
off of those irregularities which interfere with mastication. By 
its use much labour is saved, and the labour which is necessarily 
exerted when the rasp only is used is thus happily avoided. 
This instrument I have termed a POSTERIOR REPELLER. 
It must not be supposed, although I am giving a code of in- 
structions as to the manner in which those instruments ought 
to be applied, that they will all be able to be brought to bear 
in strict accordance with my explanations; for, of course, the 
irregularities encountered in the diseases and growth of the 
teeth will be various, and the instruments, therefore, must be 
selected by the operator for the required purpose, and his own 
judgment or tact must be exercised. But I have no doubt that, 
with the instruments I have this evening laid before the Asso- 
ciation, you will be able to contend with, and to operate upon, 
such forms of disease as have hitherto baffled us. You will 
recollect I have before stated that it is necessary, in the removal 
of any portion of a tooth which has become elongated, to get a 
bearing or force behind ; and it has been my particular study to 
make such instruments as would enable us to effect this object. 
The purpose of my present inventions is to prevent any injury 
or pressure being conveyed to the bloodvessels supplying the 
tooth, for without this precaution the vessels of the pulp might 
be so lacerated, that necrosis or death would follow. Such 
serious injury as this adverted to might be done not only to the 
tooth we are operating upon, but also to any other tooth that 
might receive the shock ; inflammation, followed by suppura- 
tion and absorption of the alveolar process, would be likely to 
ensue, and consequently a loosening of the tooth. 
The next instrument is a chisel, to which I lay little claim 
for merit, as it is like the common or ordinary one in use, with 
this slight difference, — it is somewhat longer and stronger than 
the common chisel known to veterinary practitioners, and is 
bevelled only on one side, so that its flattened surface is brought 
in contact with the tables of the teeth, thereby enabling us to 
make our fracture the closer. This chisel, however, must be 
