Injurious Effects of the Roentgen Rays Page 9

and tested for platinum, as already indicated. The color reaction was characteristic, intense and permanent, in fully 20 c.c. of solution. This experiment proves conclusively that the particles of platinum are not projected into surrounding objects.

It is of quite recent demonstration (20) that the silver salt of the photographic plate which is sensitive to white light, is not affected by the x-rays. Experiments made upon the sensitized collodion film and the Daguerreotype plate produced no image whatever, while upon the gelatin coated plate or film the negative image was produced in the usual manner.

The conclusion drawn was that the x-rays did not produce an electrolytic effect upon the silver salt, nor even the partial decomposition as produced by ordinary light directly; but they did produce a fluorescence of the gelatine film and perhaps of the glass support, if it were of a fluorescent material, which in turn acted upon the silver salt suspended in it, just as ordinary light does. Incidentally the statement was made that plates most sensitive to ordinary light are not necessarily most sensitive to the x-rays, since the result depends upon the kind of gelatine used, and the period of cooking to which the emulsion was subjected. This fact was apparently confirmed by a series of comparative tests conducted by the writer in which he was convinced that the particular brand of plates which happened to be cheapest in the market produced the best x-ray negatives in the shortest time of exposure.

Little attention has been given to the comparative value of the static and induced currents in the production of the x-rays, and it may be worthy of note in this connection that in the great majority of cases reported as "x-ray burns," the current has been generated by the induction coil apparatus. Such an equipment of high potential, even a ten or twelve-inch spark-gap, requires less room, and is less expensive; but the current is characterized by much greater amperage than the static current of the same or even greater potential in volts. The amperage of the static current is very low, while the potential is almost unlimited under proper conditions. Also the distance of the exposed part from the tube in those reports which mention the distance has been invariably small, from three or four to six or eight inches.

The length of the spark-gap is directly proportional to the internal resistance of the tube (21), and is also directly dependent upon the voltage (22), and not the amperage. The greater the internal resistance, the more penetrative are the x-rays produced. Thus it is seen the production of x-rays of the highest penetrative value is directly dependent upon the voltage utilized. And consequently, the lower the amperage, the less danger attends the use of the tube, because a less quantity of electricity per unit of time is free to act upon the tissues; and with a current of higher potential and lower amperage the greater may be the distance from the tube, and only the voltage is important to produce x-rays.

Since the intensity of the x-rays varies inversely as the square of the distance, it follows that the higher the potential in volts, the greater may the distance be, to produce the same results of penetration. I have not been able to see any penetration by the skiascope, from a tube supplied by an induction coil having a six-inch spark gap at a distance of eight feet. While with a tube supplied by the static machine working at a similar sparking interval, the bones of my hand could be seen at a distance of thirty-six feet.

Professor Thomson has already demonstrated that a "burn" may be induced by the use of the static current in the vacuum tube, but no cases on record, to my knowledge, in which injuries have