PREFACE. To fill a demand for an inexpensive non-mathematical work on the subject of radium and its application in medicine, arrangements were niade for the publication of this book. At that time the excellent treatises of Rutherford and Soddy had not appeared. To anyone purposing the prosecution of investigations, these works are indispensable. One treats the phenomena of radio-activity from the point of view of a physicist, while the other looks at them more with thte eyes of a chemist. The appearance of these works has made it necessary to alter this book somewhat. The technical details have been given so admirably by these CO-laborers that it has been thought just as well to omit much here. This book emphasizes a phase naturally but hinted at by them, namely, the application of radio-active substances in medicine. The writer is not in a position to harillonize the contradictory evidence given in reputable medical journals as to the therapeutic uses of the salts of radium, consequently the observations have been iinpartially reported. Physicians of prominence, who have had much to do with the use of this novel substance in their practice, have been good enough to revise the chapter bearing upon that phase of the subject. It has been deemed advisable for comparison to annex a short chapter on other therapeutic radiations. As many physicians will have neither the time nor the opportunity to study the larger works, sufficient of the general subject has been presented for a fairly clear conception of-our present knowledge of these startling, perhaps revolutionary, phenomena. illthough the work makes no prctelistx at completeness, all known sources of information have ljern irrcl. t l r a - u l o l. In most cases tlue credit has Ijeen given. The ljihliograljli-, vIiich -as prel aretl, has Ijeen o iiitted. r most coiiiplete index to the e t e n i - licte rature of ratliurn 11y l r. George 1. Icunz is in prt. ss for the 17nitecl Statrs Geological Survey. 1 s. Fritz erhall ant1 l l r . Prc lcric 1 l . t I reitlit tI iavc, Kenerously followed the proof-sheets. Mr. S. l. rahan n. as good enough to prepare the intles. TABLE OF CONTENTS. - Chaptyr Page I. The l- heno nenono f Radio-Activity, . . I 11. The Extractiori of Radiutll Salts Properties, Physical ancl Chemical of Radiuni, . . 22 111. Other Radio-Active Substances IJra li umT, h orium, Polonium, Actini un. Cnrolinintn, Thoriutn X, Radio-Telluriuni, Htilaniunl, and Radio-Active T, ead. The Sources of Radio-Activity, . . 46 I The Emanations of Radium and Induced Iiadio-Activity. Ex-Radio, 69 L, The Theories of Radio-Activity, 94 VI. The Physiological Properties ancl Therapeutic Applications of Radio-Active Substance, . I I 5 VII. Other Therapeutic Radiations, . . I42 Index, 153 Radium and Radio-Active Substances. .. CHAPTER I. THE PHEKOMEKON OF RADIO-ACTIVITY. If there be one thing which Inay be said to characterize science and its progress, it is evolution, or growth. Practically all the great movements of science and its tnodern marvels are linked to the past. The phenomenon of radio-activity, which has astotlished a civilization accustomed to wonders, is no excttptlon. Without going loo far back, attentioll may be called to the now well known fact that an electric spark passes through the air in a zigzag line, the length of tvl ich varies with the distance between the charged and uncharged bodies...