RADIUM RAYS 223 



velocities. The smallest of these particles, one one-thousandth the 

 size of a hydrogen atom, bear negative charges (or, shall we say, are 

 negative charges) of electricity, and are called electrons. They travel 

 with about 95 per cent, of the velocity of light, penetrate " opaque " 

 bodies, passing easily between and through their atoms, darken a photo- 

 graphic negative, and to a slight extent ionize a gas through which 

 they pass. Streams of these particles constitute the fi rays of radium 

 and other radioactive substances. 



The larger particles projected from radioactive bodies are about 

 twice the size of a hydrogen atom, or two thousand times as big as the 

 /3 particles. They move more slowly than the latter, and carry a 

 charge of positive electricity. On account of their relatively greater 

 size, they are much more effective ionizers, and correspondingly less 

 penetrating to " opaque " matter than the ^ particles. They were 

 named a particles by Eutherford. Streams of them constitute a rays. 



Whenever a [3 particle, or electron, is started or stopped a pene- 

 trating electro-magnetic pulse in the ether (X ray) is developed. 

 Such rays proceeding from radium are called 7 rays. In addition to 

 the emission of one or more of these three kinds of rays, radioactive 

 materials give off a radioactive gas, called the emanation. In study- 

 ing the physiological effects of radium, therefore, we have to consider 

 these four factors — a rays, /3 rays, y rays and emanation. 



Our interest in the effects of radium rays on living organisms is 

 enhanced by the discovery that radioactivity is widely distributed in 

 nature. It is probable that all plants and animals are adjusted to a 

 normal degree of radioactivity in their environment, or, in other words, 

 are in a state of radiotonus. Professor J. J. Thomson was the first 

 to discover that air bubbled through Cambridge (England) tap-water 

 became decidedly radioactive, and the subsequent researches of numer- 

 ous other physicists have taught us that this property belongs to the 

 waters of most deep wells, to mineral waters generally, to freshly fallen 

 rain and snow, to the spray at the foot of waterfalls, to the water of 

 the ocean in certain localities, and quite probably to all spring waters. 



After Elster and Geitel found radioactivity a property of the 

 " fango," or mud from the hot springs of Battaglia, in northern Italy, 

 other investigators discovered the same property in mud from various 

 widely separated sources, in lava from volcanoes, in the sediments of 

 springs, the sand of the seashore, and in sedimentary rocks. 



The discovery, also made by Elster and Geitel, of the presence of 

 radioactivity in the earth's atmosphere has been abundantly confirmed. 

 Soil-air is more strongly radioactive than air above the surface. Evi- 

 dence leads to the conclusion that the radioactivity of water, air, mud, 

 rocks, etc., is due to the presence of the emanation of radium and other 

 radioactive substances. 



Eadioactivity, therefore, must be recognized as a factor of plant 



