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POSITIONS AT THE CHAIR. 57

ing upright with his elbow at his side. The range of one-half
of the humerus will be quite sufficient for all ordinary operations
in any part of the mouth. Only a few things out of the usual
order may require different positions.
Adjustments of the patient must be made to facilitate oper-
ating at this particular height. If the patient is to sit upright
for operations on the lower teeth, the chair will be correspond-
ingly low. If, on the other hand, the chair is thrown far back
for operations on the upper teeth, this movement brings the
patient's head lower, and the chair should be raised to corre-
spond in order that the field of operation may come to the proper
height. The patient's head must be turned to one side or the
other, to bring the particular part of the mouth desired into
view, so that operations may be performed easily. If the field
of operation is too low, too much bending of the back is required.
If too high, the arms must be raised. Either one of these posi-
tions becomes tiresome to the operator, but of the two, holding
the hands up is much the more tiresome, and will break the man
down faster. The object is to find those positions in which the
operator can work many hours with the least fatigue, month after
month for years together. This is of especial importance from
the point of the continued health and endurance of the dentist.
Otherwise than height there are four positions of the oper-
ator at the chair which are best defined as: (1) Right side in
front, Figure 34 for the upper, and Figure 39 for the lower teeth.
In this position both of the operator's hands are at the front or
side of the patient's mouth without passing the left arm around
the patient's head. In each case the position is defined by the
position of the operator's hands rather than the actual position
of his person. (2) Right side behind, Figures 35, 41. In this
position the left arm is passed around or over the head of the
patient. (3) Left side behind, Figures 36, 44. The right hand
is around or over the head of the patient. (4) Left side in front.
Figures 37, 45. In this both hands are in front of the patient
on the left side. These four positions for the upi^er and four
positions for the lower teeth, form the basis for all definitions
of the operator's position at the chair. In the exhibit of finger
and instrument positions in which the hands and a part of the
face only are shown, the actual position of the operator will be
easily read. Besides the instruction in position, it affords a
language, or nomenclature of positions which may be of especial
use in all teaching, whether in school or society work.
In the group of pictures several have been selected that are
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