ular end of the esophagoscope as measured by the rule is 20 cm., we
subtract this 20 cm. from the total length of the esophagoscope (45
cm.) and then know that the distal end of the tube is 25 cm. from the
incisor teeth. Graduation marks on the tube have been used, but are
objectionable.

[FIG. 7.--Measuring rule for gauging in centimeters the depth of any
location by subtraction of the length of the uninserted portion of the
esophagoscope or bronchoscope. This is preferable to graduations
marked on the tubes, though the tubes can be marked with a scale if
desired.]

_Batteries_.--The simplest, best, and safest source of current is a
double dry battery arranged in three groups of two cells each,
connected in series (Fig. 8). Each set should have two binding posts
and a rheostat. The binding posts should have double holes for two
additional cords, to be kept in reserve for use in case a cord becomes
defective.* The commercial current reduced through a rheostat should
never be used, because there is always the possibility of "grounding"
the circuit through the patient; a highly dangerous accident when we
consider that the tube makes a long moist contact in tissues close to
the course of both the vagi and the heart. The endoscopist should
never depend upon a pocket battery as a source of illumination, for it
is almost certain to fail during the endoscopy. The wires connecting
the battery and endoscopic instrument are covered with rubber, so that
they may be cleansed and superficially sterilized with alcohol. They
may be totally immersed in alcohol for any length of time without
injury.

* When this is done care is necessary to avoid attempting to use
simultaneously the two cords from one pair of posts.

[FIG 8.--The author's endoscopic battery, heavily built for
reliability.

It contains 6 dry cells, series-connected in 3 groups of 2 cells each.
Each group has its own rheostat and pair of binding posts.]

_Aspirating Tubes_.--Independent aspirating tubes involve delay in
their use as compared to aspirating canals in the wall of the
endoscopic tube; but there are special cases in which an independent
tube is invaluable. Three forms are used by the author. The "velvet
eye" cannot traumatize the mucosa (Fig. 9). To hold a foreign body by
suction, a squarely cut off end is necessary. For use through the
tracheotomic wound without a bronchoscope a malleable tube (Fig. 10)
is better.

[FIG. 9.--The author's protected-a