The advance of photography : its history and modern applications (1911)

RONTGEN-RAY PHOTOGRAPHY 353 Lead-lined boxes are sometimes used to protect the plates while they are in the room where the X-rays are working ; these are useful and reliable if the lead-lining is of sufficient thickness. It should be at least 1*5 mm. thick. It is customary to enclose the sensitive plate when required for exposure in a light-tight black envelope, and to dispense with the usual dark slide. The plates, if purchased in the necessary black envelope, are always placed with their films towards the plain side of the envelope, and this should therefore be placed towards the object being radiographed. If this is not done and the overlapping gummed parts are placed toward the object, marks on the developed plate will indicate the presence of the gum, etc. The tube should always be at a sufficient distance from the plate to ensure as small an amount of distortion as possible. The distance will vary with the object being radiographed, but it is rarely advisable to place the tube less than 12 to 18 inches from the plate when photographs of parts of the human body are required. Sometimes it is found advisable to use a barium platinocyanide screen to intensify the effects. In this case, a dark slide of some form or other must be used, for the screen must be so placed as to be in actual contact with the film during exposure. Of course when the ordinary wooden dark slide is used, and is placed in position, it is not necessary to open it in order to make the exposure, for wood is sufficiently transparent to the rays. It may be well to remember that with reference to these rays, bone is the most opaque substance in the human body ; the blood is much more opaque than the flesh, hence anaemic patients need less exposure than full-blooded persons. The liver and stomach are fairly opaque to the rays, and it is noticed that the muscles, when tense, are more opaque than when they are relaxed.