SCIENTIFIC IMPORTANCE OF X-RAYS—GARLAND 189 
duct between the liver and gall bladder is not blocked and you remain 
fasting. This test is a valuable method for the detection of non- 
opaque cholesterin stones in the gall bladder; indeed, it is the only 
method by which such may be diagnosed preoperatively. 
Cardiovascular system.—The accurate determination of heart size 
in the living human being can be made only by roentgenological meth- 
ods. It is to be noted, in passing, that this is not always a very im- 
portant factor, since cardiac function rather than size governs most 
healthy lives, and function can be assessed by many means much more 
accurate than roentgenologic ones. However, the problem of heart 
size does come up in some individuals and Roentgen methods are then 
invaluable. Correction should always be made for the amount of 
magnification present, the phase of respiration in which the patient 
happens to be during the exposure, and similar items. As in the case 
of the alimentary tract, complete examination of the cardiovascular 
system involves both fluoroscopy and roentgenography. In recent 
years the use of opaque substances has permitted the outlining of the 
individual heart chambers in the roentgenogram and the study of the 
circulation in a manner one could scarcely have even dreamed of 50 
years ago. Besides giving information concerning the size, shape, 
position, and mobility of the heart, Roentgen methods also may dis- 
close the presence or absence of coronary disease and its sequelae. 
Records of the beating heart may be obtained on a single film by 
means of kymographic apparatus and deductions as to the presence of 
localized areas of heart-muscle disease deducted therefrom. The con- 
dition of the arteries and veins in the extremities can be studied by 
means of both plain films and films made with contrast media and 
the presence of varicose veins in the deep venous circulation of the leg 
can be detected and unnecessary operations avoided. 
Central nervous system.—Medical advances in the diagnosis and 
treatment of diseases of the brain, spinal cord, and peripheral nerves 
is one of the most interesting chapters in modern science. The normal 
brain casts no distinguishing shadow in the routine roentgenogram. 
However, by very simple methods, its outlines can be revealed. This 
consists of performing a spinal puncture (in the lower portion of the 
back), withdrawing from 75 to 150 cubic centimeters of cerebrospinal 
fluid, and injecting in its place a corresponding amount of air. Upon 
placement of the patient in an erect position this gas will ascend 
into the cerebrospinal fluid pathways around, between, and in the 
various lobes of the brain. Several plain or stereoscopic roentgeno- 
grams then are made from various angles, with the patient both erect 
and horizontal. The air absorbs during the next few days and is 
replaced by normal fluid. By this method various types of brain in- 
jury, brain disease, and tumors may be detected. Considerable ex- 
perience is desirable in interpreting these pneumo-encephalograms. 
