ody because one
is not seen. Even metallic objects are in rare cases exceedingly
difficult to demonstrate.

[FIG. 75.--Radiograph showing pathology resulting from complete
obstruction of a bronchus with atelectasis and drowned lung resulting.
Foot of an alarm clock in left bronchus of 4 year old child. Present
25 days. Plate made by Johnston and Grier.]

_Positive Films of the Tracheo-bronchial Tree as an Aid to
Localization_.--In order to localize the bronchus invaded by a small
foreign body the positive film is laid over the negative of the
patient showing the foreign body. The shadow of the foreign body will
then show through the overlying positive film. These positive films
are made in twelve sizes, and the size selected should be that
corresponding to the size of the patient as shown by the
roentgenograph. The dome of the diaphragm and the dome of the pleura
are taken as visceral landmarks for placing the positive films which
have lines indicating these levels. If the shadow of the foreign body
be faint it may be strengthened by an ink mark on the
uncoated side of the plate.

[FIG. 76.--Partial bronchial obstruction for long period of time
Pathology, bronchiectasis and pulmonary abscess, produced by the
presence for 4 years of a nail in the left lung of a boy of 10 years]

_Bronchial mapping_ is readily accomplished by the author's method of
endobronchial insufflation of a roentgenopaque inert powder such as
bismuth subnitrate or subcarbonate (Fig. 77). The roentgenopaque
substance may be injected in a fluid mixture if preferred, but the
walls are better outlined with the powder (Fig. 77).

[FIG. 77.--Roentgenogram showing the author's method of bronchial
mapping or lung-mapping by the bronchoscopic introduction of opaque
substances (in this instance powdered bismuth subnitrate) into the
lung of the patient. Plate made by David R. Bowen. (Illustration,
strengthened for reproduction, is from author's article in American
Journal of Roentgenology, Oct., 1918.)]

ERRORS TO AVOID IN SUSPECTED FOREIGN BODY CASES

1. Do not reach for the foreign body with the fingers, lest the
foreign body be thereby pushed into the larynx, or the larynx be thus
traumatized.
2. Do not hold up the patient by the heels, lest a tracheally lodged
foreign body be dislodged and asphyxiate the patient by becoming
jammed in the glottis.
[143] 3. Do not fail to have a roentgenogram made, if possible,
whether the foreign body in qu