190 § ANNUAL REPORT SMITHSONIAN INSTITUTION, 1946 
The spinal cord may be studied by similar methods, or by the injec- 
tion of radio-opaque contrast media into various portions of the spinal 
canal. The media most commonly used at the present time are prepara- 
tions containing iodine (iodized poppy-seed oil and ethyl iodophenyl- 
undecylate). About 8 cubic centimeters of the opaque oil are injected 
in the lower lumbar area and the patient is fluoroscoped on a special _ 
table. By tilting the body up and down, the lake of opaque oil can be 
made to traverse the spinal canal. Indentations and certain other 
alterations of its shadow will disclose the presence of ruptured disks, 
tumors, and so forth. 
Genito-urinary system.—It is now possible to examine the cates 
of virtually every portion of the genito-urinary system. One can de- 
termine the function of each kidney following intravenous injection 
of an iodine salt selectively excreted by the kidneys. The seminal 
vesicles and ducts may be outlined by contrast media. Similarly, the 
cavity of the uterus and the slender canals of the fallopian tubes can 
be shown. In this manner an extraordinary variety of conditions, 
normal as well as abnormal, may be detected. The number, size, and 
approximate age of infants in utero may betold. The exact alterations 
in the shape of the fetal bones during the actual process of birth have 
been studied by serial roentgenograms. The remarkable molding and 
elongation of the fetal skull have been shown, as well as the disposition 
of the fetal limbs and placenta. The latter has been studied by arterio- 
graphic injection of opaque media and valuable information as to the 
uniovular or multiovular nature of twins ascertained. Abnormal ges- 
tations have been diagnosed correctly in time to save the mother an 
unnecessarily prolonged pregnancy or labor. These cases are some of 
the most tragic incidents that a radiologist encounters. The normal 
fetal skeleton does not contain sufficient calcium to cast a clear shadow 
in routine roentgenograms before a gestation period of 12 weeks. 
Within increasing accuracy after that time the fetal parts may be 
shown. Attempts have been made to determine the sex of the fetus 
by X-ray methods, but no practical method has yet been found. Exten- 
sive studies have been made on the influence of the shape as well as 
the size of the female pelvis on spontaneous delivery. Female pelves 
are classified into four general types, based on their shape. By careful 
Roentgen examination, the probability of easy or difficult labor can 
be prognosed with considerable accuracy in selected cases. 
Osseous system (bones and joints).—The first use of X-rays was 
in the examination of cases of suspected fracture. From that day 
its uses have been extended to include the study of bone growth, bone 
tumors, joints, tendons, bursae, and adjacent structures. In the cor- 
rect diagnosis of all bone conditions, and in the treatment of many 
of them, X-rays are essential. 
