Radium does not combine chemically with any known substance in the body. The therapeutic effects are indirect. When the electrons are ejected with great speed from the atoms of the radioactive salts, they pass through millions of other atoms, knocking out new electrons as they go, leaving the atoms with a positive charge, in which condition they are called “ions.” These positively charged particles at once enter into new combinations, new chemical unions, which produce new substances. But these may be injurious to the normal tissues as well as to the cells of the disease which it is desired to destroy. In some cases, the diseased cells are more susceptible to the rays than are the normal cells, in which instances the growth of the abnormal or diseased cells may be retarded, or they may even be totally destroyed. It is thus seen that application of the rays may result in alleviation of the disease, or, possibly, effect a complete cure, as the case may be. The action of radium on various (colloidal) substances is now well understood from the point of view of the biophysicist; but this phase of the subject is too highly technical for exposition in a book intended for popular circulation. While it is fully recognized that there are quite definite limitations to the efficacy of radioactivity in its application to disease, as a matter of fact the use of radium as a therapeutic agent would be much more extensive were it not for its high cost and scarcity. No one questions its exceptional value in the treatment of certain diseases, and a method will probably be discovered, in the near future, by which it may veritably be used to postpone the age of senility. A young man who had read somewhere that radium is a sure cure for any and all of the ills to which flesh is heir, entered a drug store and asked: “How much is radium an ounce?” The druggist smiled, and named a figure which made the young man blink. “Not really?” observed the prospective customer. “Then you may give me an ounce of cough lozenges.” Until quite recently, an ounce of radium cost almost as much as 3¾ tons of gold! That is to say, an ounce of radium, if this much could be purchased “off hand”--which it couldn’t--would cost about $2,500,000. The price was at one time $3,000,000 an ounce. When we speak of “radium,” we really mean--or ought to mean--_radium salts_. Pure radium soon abandons its metallic form by entering into chemical combinations. It is the purified radium salts that cost, as late as 1923, $2,500,000 an ounce--the price of ¾ of a ton of platinum, the most “precious” of all the metals excepting radium. In 1920, radium was 200 times more valuable than an equal weight of pure blue diamonds, and 180,600 times as valuable as gold. A cubic foot of the salts--had this amount been obtainable--would have been worth $7,000,000,000.