SCIENTIFIC IMPORTANCE OF X-RAYS—GARLAND 181 
diseases of mummies may be determined without opening the wrap- 
pings or even the sarcophagi. Genetics has been furthered by study- 
ing the behavior of many species, notably Drosophila melanogaster 
(the common fruit fly) following exposure to specific quantities of 
X-rays (with the production of subsequent mutations of certain 
types). 
Physiology is greatly indebted to roentgenologic methods, notably 
in connection with the study of the alimentary tract, the circulation of 
the blood, and the functioning of moving parts, especially joints. 
X-ray “movies” as well as fluoroscopy and “still” films have been 
used extensively in this field. As an example of their value in one 
small department the X-ray (kymographic) determination of ~ 
cardiac output can be cited (2).5 
An X-ray film is made of the subject’s chest, in the erect position, 
at a measured distance (say 5 or 6 feet), using a lead grid between the 
patient and the film. The exposure takes about 2 seconds’ time and 
the film is moved slowly downward a distance of 12 millimeters dur- 
ing the exposure. When the film is dried, the outline of the heart 
appears as a serrated border, the “peaks” representing the shadow in 
maximum expansion and the “valleys” in maximum contraction. The 
peaks are joined by one line, the valleys by another. The rest of the 
heart shadow is completed as shown in plate 1, figure 1. The area in 
these two phases then is measured with a planimeter and the figures 
corrected for distortion. The corrected figures then are converted into 
volumes according to a table established from experimental and ca- 
daver work. The difference in volume between expansion and contrac- 
tion gives the output per beat. In many normal subjects the average 
stroke output per ventricle is 60 cubic centimeters; a person with a 
rapid pulse tends to have a smaller, and one with a slow pulse a cor- 
respondingly larger output. Therefore, it is more informative to 
speak of the output per minute than the output per stroke; this in 
turn varies with body size, which may be expressed fairly simply in 
terms of total body surface. The number of liters of blood pumped 
per minute per square meter of body surface is termed the cardiac 
index. This index thus may be found by using this particular X-ray 
method. (Needless to say, there are other methods of determining 
this index, but the roentgenkymographic one is a simple and reliable 
one when correctly used.) 
Our knowledge of the functions and behavior of the alimentary 
tract in health and disease is largely dependent on the use of Roentgen 
methods of examination. Some of the earliest investigators in this 
field have been American physiologists who did their original work 
on cats (to whom they fed bismuth in milk, and so forth). Food also 
* Numbers in parentheses indicate references at end of article. 
