The use of stabilized thorium dioxide sol (thorotrast) for roentgen visualization of the liver and spleen has become a well established clinical procedure, but the question of its radioactivity and the resultant effect on the reticulo-endothelial system is far from settled. The manufacturer places a warning in each box stating that the matter should be seriously considered.
Many observers have asserted that the radioactivity of this preparation is negligible as it causes no fogging of a film in many hours' time, but this is far too crude a method of detecting small quantities of radiation.
The Geiger counter.1 when brought in the vicinity of a sample of thorium dioxide sol, showed such violent and immediate response that I at once realized that I had a means of making observations of comparatively high accuracy. Though the instrument described is capable of making only gamma ray tests, it is substantial and