. The American journal of roentgenology, radium therapy and nuclear medicine . was insulated from the screen bymeans of black paper of sufficient opacityto prevent the fluorescence from affectingthe sensitive emulsion, but not of sufficientopacity so that its roentgen ray absorptionwas of moment. A unit exposure wasthen determined, being that which justimpressed a noticeable image on the half of the plate not covered by theblack paper was then protected by a pieceof lead. The remaining unprotected areawas then given a series of exposures in one inch strips, increasing regularly in mu
. The American journal of roentgenology, radium therapy and nuclear medicine . was insulated from the screen bymeans of black paper of sufficient opacityto prevent the fluorescence from affectingthe sensitive emulsion, but not of sufficientopacity so that its roentgen ray absorptionwas of moment. A unit exposure wasthen determined, being that which justimpressed a noticeable image on the half of the plate not covered by theblack paper was then protected by a pieceof lead. The remaining unprotected areawas then given a series of exposures in one inch strips, increasing regularly in multi-ples of the unit exposure. After exposing the last step, the half ofthe plate in direct contact with the intensi-fying screen was given one unit plate was then developed under stan-dard conditions. One-half of the materialthen showed a density resulting from theexposure to one unit with the screen andthe other half showed densities rangingfrom one just noticeable to one nearlyopaque. It was then a simple matter tomatch the density of the unit exposure with. A. Unit Exposure with Multiples of Unit Exposure without Screen. the screen, with some particular step onthe graded strip made without the the illustration given, this unit exposurewith the screen matched step No. 3 on thegraded strip without the screen. The screen 458 The Roentgen Study of \isceroptosia 459 can thus be stated to have a speed factorof three since it requires three times theexposure without the screen to give thesame density as with the screen. For the purpose of the experiments inquestion, the unit exposure referred to wasone second at 30 inches distance, 23^-2 milli- amperes, 5 inch spark gap, using EastmanDupli-Tized X-Ray Film, and standard de-velopement was five minutes at 65 degreesin a standard Metol-Hydrochinon thanks are due to Mr. Millard for his helpful criticism and aidto suggesting improvements in the text. THE ROENTGEN STUDY OF VISCEROPTOS
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