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HISTORY OF DENTAL SUEGERY 239

any, rosewood, or some otiier heavy material, that it may be rendered solid and
firm, capable of bearing the parts which are to be attached ; the seat should
be broad and roomy, at least two feet by twenty inches. This being the most
important part will be hereafter described more particularly. The back should
be nearly four feet in height, and movable by hinges attached to tlie lower part
of tlie frame-work of the seat ; it should be capable of falling Ijackwards, com-
pletely horizontal, or remaining at any angle, which the operator may require.

Operating Chair.

"This latter point is attained by a piece of brass, formed in the segment
of a circle, one end being attached to each side of the frame-work of the back
board, the other part being made to pass through the post of the arm of the
chair. This piece of brass must be perforated with holes, at the distance of
an inch from each other : a brass bolt passing tlirough the post and through
one of the holes, according to the angle required, will hold the back firmly.
The position may be changed in a moment, by the simple removal of the bolt
to any other hole, which will enable the operator to place the patient in every
'••priety of position, from tlie perpendicular to the horizontal. This is partic-
ularly useful in cases of sudden fainting.
"At about one foot from the top, the back of the chair should be divided,
and made capable of falling down, by hinges. These hinges should be so
constructed that their lower parts should not be fixed, but allowed to fall into
sockets, so that the upper part of the back ma}', when required, be removed