STUDIES ON X-RAY EFFECTS. X. THE BIOLOGICAL ACTION OF SMALL DosEs oF Low FREQUENCY

Attempts have been made in this laboratory to compare the biological action of the soft or low frequency and the hard or high frequency x-rays, but the impossibility of comparing doses of the two types of rays with our present apparatus and measuring devices has rendered the results of these studies of little value. However, by varying the doses of the soft and hard rays there is one point which seems definite; namely, that with the softer rays it is possible to induce an apparent stimulation of the lymphoid cells which is preceded by only a very short and transitory period of depression. '-4 With the harder rays the stimulation phase is less pronounced, if present at all in the dosages employed by us. Russ, Chambers, Scott, and Mottram s have succeeded in bringing about an increase in the circulating lymphocytes of rats by repeated small exposures to x-rays described by them as being of "medium" or "medium soft" quality. Our first satisfactory results were obtained with the tube operated at a spark-gap of about l1⁄2 inches. Later experiments with a spark-gap of about ~ inch gave a more uniform and pronounced reaction. The present study has to do with the effect of still softer x-rays than those used in previous experiments. For the generation of these