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RONTGEN-RAY PHOTOGRAPHY 357
be got when a tube is working under the best conditions as to degree of hardness, and there can be no hesitation in saying in which of the three illustrations those qualities are the most clearly marked.
The last shows the result obtained with a very hard tube, that is one in which the vacuum has been pushed as high as it is possible to obtain radiographs with, and here it is apparent that even the more dense parts are relatively transparent to the rays, hence the radiograph obtained is far from satisfactory.
These photographs were all taken with the same tube (Cox Record). The different effects were obtained by altering the time of exposure, thus Fig. 159 had an exposure of 2 seconds, Fig. 160 of 7 seconds, and Fig. 160a of 30 seconds. The results correspond to those which would be obtained with soft, correct, and hard tube respectively. A 10 inch Cox coil with the Cox Radial break, was used. The voltage was 100, primary current 1 ampere, current through the tube J milliampere, and the equivalent spark gap was 3J inches. Similar effects would be obtained by correct exposure with tubes requiring about 2, 3 J, and 5 J inch gaps respectively. The photographs were obtained on Ilford plates, placed at a distance of 15 inches from the tube.
Great care must be observed on the part of the operator, so as to shield himself and also the patient from the access of the rays, as very dire consequences may result from carelessness in this respect. The necessity for such precaution has been made apparent to every reader by the numerous cases of victims, suffering from Rontgenray dermatitis, which have been recorded in our daily papers.
Any ordinary developer may be used for these negatives, but it should be clearly understood that the negatives ought not to be over-developed, and it is best to use weak developers.