Further Studies in the Effectiveness of Different Wave Lengths of Radiation1
Journal - Radiology
IN a recent number of the American Journal of Roentgenology and RadiumTherapy (1924, XII, 474) I published a paper giving some preliminarystudies of the effects of two different wave lengths of X-ray onstandard animal tumors and showed that with equal ionization dosage,when the chamber was of the Duane type, the tumors were killed atapproximately the same time. These experiments have now been extendedto another type of tumor with the same result, and a résuméof some of the more recent findings may be of interest. I refer tothat paper for the details of the production of the X-ray and thenitration.
One of the peculiar advantages of using animal tumors in this typeof study is obvious, as it is possible to determine the death-pointwithin the accuracy of any biological experiment. If tumors are inoculatedafter exposure to X-rays, and grow, they are evidently not dead;if they do not grow, they evidently are dead. This avoids the useof any reagent or morphological change in the cells for the determinationof their viability.
For example, the decolorization or non-decolorization of methyleneblue has been used by von Wassermann as a test for cell-death afterradiation, but even if such color change is reliable, and its valuehas been denied of late, a few cells might be still alive and yetnot furnish sufficient mass of tissue to decolorize the whole bulkof fluid. Just the same, a recurrence would be due to these few remainingcells.
Again, the employment of vital stains for microscopic determinationof the viability of cells is attended with gross errors. The minutehistological structures of cells are not altered by X-ray in a characteristicmanner, so that no conclusions can be drawn from this aspect.2
The determination of the effect of radiation of bean seedlings aspractised by Jüngling3 again depends upon many conditions otherthan the death of all the cells, for the rays may wholly preventor seriously check growth whether a large number or a small numberof cells be destroyed. The same complications affect the use of thedeath-point of mice, proposed as a test by Meyer and Ritter,4 andthe results are quite variable and unreliable.
Further obvious convenience of animal tumors is that such thin slicescan be employed in the radiation tests that but little absorptionof the rays takes place in the tissue used. A millimeter of the softsubstance of the tumor has almost no absorptive power at the voltagesordinarily used, certainly no more than a meter of air.
Chart I shows the curve of absorption with different wave lengthsfor a millimeter of tissue. Obviously absorption and scatter areboth included.
The curve for air absorption of X-rays at the same wave lengths practicallycovers that for tissue at short wave lengths, if the difference indensity between air and tissue is taken into consideration.