Biological Effects of Penetrating Radiations 85 



The effects produced by radiations in their passage through 

 Hving matter may be studied in two ways. The investigation 

 may be concerned with the mechanism of the action of radiation 

 by means of specially designed experiments on selected materials, 

 usually of the simplest kind. This is often referred to as 

 * 'fundamental research," and is a long-term program of research 

 in which much detailed information is gradually collected for a 

 particular material, but it does not necessarily follow that what 

 is observed for one tissue applies to other kinds of tissue after 

 similar doses of irradiation. The other, or short-term method, 

 involves a study not of the exact mechanism of the biological 

 action of radiations, but of their histological effects under given 

 physical conditions. Much of this work forms the background 

 of medical radiotherapy, and its results are no less fundamental 

 than those obtained by the other approach ; they are sometimes 

 of great practical use. 



It was natural, perhaps, that the physicists should be attracted 

 to problems concerned with the mechanism of action of radiation 

 on living cells, while the biologists, in the main, devoted their 

 energies to recording changes in behavior of irradiated tissues 

 under a variety of experimental conditions. This division of 

 labor has, however, had an unfortunate tendency to sharpen 

 the difference between the physical and biological approach to 

 radiological problems. The result has been the elaboration of 

 theories of action of radiation with, at best, only a limited scope, 

 which have generated a great deal of controversy, not always to 

 the advancement of the science. Theories of action start from 

 the law of Grotthus and Draper that only absorbed radiation 

 is effective. The physical unit for absorption is the atom. The 

 biological unit is the cell, made up of some 10^^ molecules in 

 active motion, within which effective radiation energy must be 

 absorbed. Absorption of X-rays in matter produces secondary 

 electrons, and it was suggested by Dessauer^'^ that these electronic 

 energies are nonspecifically degraded on colliding with protein 

 molecules, and that the energy is transformed into the basic 

 process of heat at isolated points. 



According to Holthusen,^-- ^'' on the other hand, the energy 

 required for the radiation effects originates from the state of 



