SCIENTIFIC IMPORTANCE OF X-RAYS—GARLAND 185 
horses, greyhounds, parrots, and other domestic pets frequently are 
subjected to examination in connection with injuries, foreign bodies, 
and certain diseases. Before the development of shockproof appa- 
ratus, cats were particularly difficult to X-ray as they have a strong 
dislike for the hair-raising qualities of the corona from exposed high- 
voltage wires. 
Miscellaneous.—One of the lesser-known but more valuable uses of 
X-rays is in connection with art. Many pigments contain lead and 
other radiopaque salts and the roentgenogram of a canvas often reveals 
shadows different from those on the visible painting. Areas of over- 
painting, alterations, and erasures can be detected. The authenticity 
of some old masters has been proved and of others disproved by such 
means. <A recent refinement includes sectional radiography of the 
canvas in which, by keeping the tube and film in motion, a very fine 
layer of the painting can be registered to the exclusion of other layers. 
TasLe I.—The electromagnetic spectrum 
Range of fre- 
Type of radiation Range of wave lengths quencies 
Electrical waves___-__-_ 1,000,000 to 20 kilometers. -____.__.-__- 10°! to 104 
Riadonwavessens 2-2 225 2OstolOLOIsmetersss*. Sees see Sere Me en 10‘ to 10" 
Imfraredirayse. #22 = = 120:000itor7. 7400 angstroms*= "55555 2 104 to 10% 
Visiblerayse =. 22 === (ACOOMOLo COUR eStLOnISe y= eee 
Ultraviolet rays. .--- 3 900itors0Orangstroms=e 52202" Joes 
Dit \ fs es eee eee ee LO ito O:Ol angstroms stys2 4) tt. eae live « 
Gamma-rays.._.-_.---. Ol to: G.02tangstrom so et eee eee 
Cosmic rays.<2. 55252 000001 angstroms V2) 2 ee i ae As 
* 1 angstrom=10—‘ centimeters; 100,000,000 angstroms=1 centimeter. 
X-RAYS IN MEDICINE 
The importance of roentgenologic methods in medicine, dentistry, 
and allied sciences is increasing continually. They permit the exam- 
ination of parts of the body hitherto inaccessible to study and the 
detection of disease at a stage when it may be cured readily. ‘They ex- 
tend the physician’s eye to an incalculable distance. They are also 
of use in the prevention of disease and in its treatment. (A small 
precancerous skin nodule, keratosis, may be cured before it develops 
into a malignancy; established, localized, accessible cancer can be de- 
stroyed.) Our knowledge of many diseases such as stomach ulcer, 
lung tuberculosis, and bone cancer has been entirely revolutionized 
and reoriented since the discovery of X-rays. They have provided 
an impetus to investigation and research in preventive medicine such 
as no other weapon ever placed at the disposal of the doctor. 
One might arrange this section according to the various medical 
specialties, but I think it will be of more interest to nonmedical readers 
to consider the importance of the rays according to each of the various 
