The flashes of light seen when the Alpha rays bombard a screen of zinc sulphide, as in Crookes’ spinthariscope, are due to cleavages produced in the zinc sulphide crystals by the impact of the Alpha rays (positive ions). Each impact on a crystal produces a splash of light big enough to be seen by a microscope. In the phosphorescence caused by the approach of an emanation of radium to zinc sulphate, the atoms throw off the Alpha (helium) particles to the number of five billion each second, with velocities of 10,000 miles or more a second. If the helium projectile should chance to “crash” into an atom of nitrogen or of oxygen, an atom of hydrogen can be knocked out of it, as was discovered by Sir Ernest Rutherford, perhaps the most distinguished of Mme. Curie’s pupils. (Strictly speaking, the disintegration particles are isotropes of helium, of atomic weight 3, the atomic weight of helium being 4.) Despite its large size as compared with an electron (or Beta particle), the Alpha particle passes through a glass wall without leaving a hole behind, and without in any way interfering with the molecules of the glass. It shoots through hundreds of thousands of atoms without ever going near enough to them to be deflected from its course. CHAPTER V RADIUM IN THE TREATMENT OF CANCER The action of radium on human tissues was unknown until 1896, when Prof. Henri Becquerel of Paris, having incautiously carried a lump of pitchblende in his pocket, discovered on his skin, within two weeks, a severe inflammation, or ulcer, which was known as the famous “Becquerel burn.” As physicians of the nineteenth century were accustomed to burn out cancers with caustics, the idea occurred to them that the application of radium might prove to be an improvement on the older method. It has proved to be so, affording in many cases not only relief, but in some instances, even a cure, not only for cancer, but for many other ailments--as we shall see presently. Since that time active investigation into the action of radium on diseased tissues has been carried on, resulting in the establishment in Paris of the “_Laboratoire biologique du Radium_,” and also of the Radium Institute of Vienna, followed by the establishment of somewhat similar institutions in various other countries, notably in England and the United States. One of the most famous institutions for radiotherapy is the recently established Radium Institute of Paris, under the management of Mme. Curie and Professor Debierne. This is composed of two distinct compartments. In one the scientific properties of radium are studied, while the other is devoted to its therapeutic applications. Dr. Regaud, who is in charge of the latter department (a branch of the widely known Pasteur Institute), endeavors to cure cancer and tumors by application of radium and X-rays.