. Elementary and dental radiography / by Howard Riley Raper . B^PLATE Irig. Drawing which shows how the size of the object being radiographed may beincreased by moving it away from the photographic plate toward the X-ray Fig. 474. The Ketcham isi in film-holder. operator is responsible for any stereoscopic effect obtained from suchnegatives. 436 . IP P END IX It will be noticed in Fig. 351 that the coins shown are of slightly dif-ferent sizes; they are, however, all of the same denomination and so thesame size. The reason for the apparent difference in size is illustrateddiagramma
. Elementary and dental radiography / by Howard Riley Raper . B^PLATE Irig. Drawing which shows how the size of the object being radiographed may beincreased by moving it away from the photographic plate toward the X-ray Fig. 474. The Ketcham isi in film-holder. operator is responsible for any stereoscopic effect obtained from suchnegatives. 436 . IP P END IX It will be noticed in Fig. 351 that the coins shown are of slightly dif-ferent sizes; they are, however, all of the same denomination and so thesame size. The reason for the apparent difference in size is illustrateddiagrammatically in Fig. 473; as the coin is moved away from the platetoward the target the shadow of it cast on the plate gets larger. Fig. 474illustrates the Ketcham film-holder for stereoscopic work. The faceis marked so the holder may be removed and re-inserted in the sameposition. CHAPTER XIChe Problem of Pulp Canal Surgery and Oral infection. Before we can proceed with a consideration of theBad Canal Work. problem of pulp canal work, we must agree that there is such a thing as bad canal work —i. e., canalwork which fails to eradicate, or prevent, the formation of local foci ofinfection at the apices of the roots of the teeth.
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