710 TEXTBOOK OF ZOOLOGY 



Summary 



Biological effects are related to the type of radiation being ab- 

 sorbed. High frequency oscillations penetrate body tissues and 

 produce molecular agitation ("artificial fever"). Infrared also in- 

 creases body temperature (although more peripheral in location). 

 More resistance is offered to radiations of the visible spectrum, 

 although the energy changes involved are not extensive enough to 

 bring about striking systemic effects. Ultraviolet radiation con- 

 tains more energy and its absorption causes changes in atomic asso- 

 ciations which may have profound effects on chemical processes. 



Roentgen and gamma radiations are very penetrating and when 

 absorbed they displace electrons and produce ionization. These 

 changes are fundamental in character and may result in extensive 

 injury to cells. 



The physiological condition of cells appears to affect the reaction 

 to radiation. Embryonic and highly active cells are apparently the 

 most susceptible. 



The quantity of radiation absorbed is an important factor in pro- 

 ducing biological effects. 



The knowledge of biological effects of radiation at present offers 

 possibilities of theorizing about the origin and development of life 

 itself. The most dependable contributions, however, have been the 

 production of artificial fever by high frequency oscillations; infra- 

 red therapy ; the understanding of the importance of sunlight in the 

 production of food by plants; the role of ultraviolet radiation in 

 the -conversion of ergosterol to vitamin D ; the use of roentgen radi- 

 ation and radium emanations in increasing mutation rates which 

 has been of great value to genetical studies; the use of these radia- 

 tions in the study of embryological development; and their use in 

 the treatment of cancer, etc. 



