. 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 . nts). (Rollins.) In these tubes, one cathode stream striking the back of the target is sent out of the field. As onlyone radiant area on the target sends light to the patient, the image on the plate or screen is as sharpas when a single focus tube is used with a direct current. The tubes may be used as single focustubes with a direct current by making the target act as an anode also. This tube is the same type asthat seen in Fig. 33, which shows t
. 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 . nts). (Rollins.) In these tubes, one cathode stream striking the back of the target is sent out of the field. As onlyone radiant area on the target sends light to the patient, the image on the plate or screen is as sharpas when a single focus tube is used with a direct current. The tubes may be used as single focustubes with a direct current by making the target act as an anode also. This tube is the same type asthat seen in Fig. 33, which shows the origin and distribution of the X-rays. Exhaustion of Tube. — The vacuum tube should be exhausted to asuitable degree, and this exhaustion may be accomplished by a mercuryor mechanical pump, the tube being kept during the earher part of theprocess at about 350° F. When the proper point of exhaustion hasbeen reached the tube is sealed off. There are various precautionsthat must be taken against moisture, and in the adjustment of the tubeto the proper vacuum, but they are chiefly of interest to the manufacturerand need not concern us Fig. 36. Tube with continuous metallic conductor. (Rollins.) Arrangement for connecting Tube with Generator. — Metal stems runfrom the terminals to the outside of the tube, and are then joined, whendesired, to the wires coming from the static machine or the coil. Thepositive wire should be connected with the target; the negative with thecathode. A tube should always be in shunt circuit, and to avoid asfar as possible any danger of puncturing it the spark-gap between the 42 THE ROENTGEN RAYS IN MEDICINE AND SURGERY terminals of the coil should only be long enough to prevent the dis-charge from passing between them instead of going through the tube. Resistance of the Tube. — All vacuum tubes, even when similar inconstruction, do not allow the electric current to pass through themwith equal ease. When the current passes easily the tube i
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