. The Roentgen rays in medicine and surgery as an aid in diagnosis and as a therapeutic agent; designed for the use of practitioners and students . proper size and spread uniformly in a layer of a suitablethickness over the surface of the cardboard. The tungstate of calciumis white, and the light is more suitable for many purposes than the morebrilliant though slightly colored fluorescence obtained from the platino- X-RAY EQUIPMENT 55 cyanide of barium. Screens of the latter kind are less durable thanothers ; they are injured by pressure, and should not be kept in a warmroom ; but each kind ha
. The Roentgen rays in medicine and surgery as an aid in diagnosis and as a therapeutic agent; designed for the use of practitioners and students . proper size and spread uniformly in a layer of a suitablethickness over the surface of the cardboard. The tungstate of calciumis white, and the light is more suitable for many purposes than the morebrilliant though slightly colored fluorescence obtained from the platino- X-RAY EQUIPMENT 55 cyanide of barium. Screens of the latter kind are less durable thanothers ; they are injured by pressure, and should not be kept in a warmroom ; but each kind has its respective uses. Tungstate of Calcium Screen. — Certain of the tungstate of calciumscreens are phosphorescent as well as fluorescent — that is, in a darkroom they retain the image of an object opaque to the rays for a momentafter the tube has been shut off. They should therefore be tested inthe following way before being purchased : — After the physician has been long enough in the dark room toget his eyes into condition to see the fluorescence, the vacuum tubeshould be excited and the light from it should be excluded by covering. Kk;. 47. Tube holder closed and ready for use. the tube with a dark cloth, or by placing it in the box already piece of heavy metal should then be placed under the fluorescentscreen and held in the same position for a minute or two. While thephysician is thus observing the screen, the current should be shut offfrom the tube. If the screen has simply fluorescent properties it willinstantly become dark, but if the part protected by the metal remainsdark, and the other portions retain any brightness, the screen has phos-phorescent as well as fluorescent properties, and should be T. B. Kinraide, of the Spring Park Laboratory, Boston, Mass., hassucceeded, by his careful and laborious investigation, in making tung- 56 THE ROENTGEN RAYS IN MEDICINE AND SURGERY state of calcium screens that are without phosphorescence. Th
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