520 BIOLOGICAL EFFECTS OF RADIATION 



There is need for a careful, well-correlated study of the specific 

 and nonspecific chemical changes brought about locally and generally by 

 both specific and nonspecific damage done to cell structure by radiation. 

 Ideally this might be done by the collaboration of a biochemist, a physiol- 

 ogist, a pathologist, and a radiologist, each well versed in his field. 



SUMMARY 



In General. — The specific effects upon organs and tissues of the various 

 bands of radiation in the electromagnetic spectrum depend in general 

 upon the physical character and properties of these radiations and the 

 manner in which they are administered. The effects upon any given 

 organ or part of an organ may be general or specific. The extent to which 

 damage may occur is dependent upon the penetrating and destructive 

 power of the given band of radiation. Any given effect is primarily 

 due to direct damage to cells, and is relative to dosage, and extends over 

 the entire range from minimal damage to immediate or ultimate death 

 of the cell. In producing a specified damage to a given cell type, the 

 total quantity of the dosage, the duration of the exposure and its inten- 

 sity, and the intervals between partitions of dosage, if any, the rate of 

 growth and variations in sensitivity of the cell as well as its specific 

 sensitivity are all interrelated. Indirect or secondary damage, through 

 injury to blood vessels or circulation of cell-disintegration products is 

 possible. This is especially true of blood vessels because of the occur- 



o 



rence of late effects from wave-lengths shorter than 8 A. Repair postu- 

 lates various grades of abnormal cells developed from damaged survivors. 

 If organ cells have been extensively destroyed, capillaries and fibroblasts 

 may invade and fill up the vacant space. Late degenerative effects may 

 follow either relatively small dosage or primary healing of acute injury. 



Since damage is related to dosage of any particular band of radiation, 

 the physical properties and especially the penetrating power determine 

 the effects which may be produced. Thus ultra-violet radiation may be 

 expected to affect only the more superficial structures while roentgen 

 radiation should affect deeper structures. Much of the apparent resist- 

 ance of an organ is probably a result of the screening effect of interposed 

 tissues. The matter of the depth dose available to tissues has not been 

 worked out for roentgen and radium radiation in regard to such a sensi- 

 tivity index. In the bodies of small animals like the mouse and rat or 

 in vitro tissue experiments the dosage is probably close to that delivered 

 to the surface. In larger animals and especially in the bones the dosage 

 may be quite different. 



In Particular. — A sensitivity index can be constructed roughly, 

 for roentgen radiation. Taking all factors into consideration one is 

 impressed by the high relative sensitivity of the bone-marrow cells and 

 intestinal crypt epithelium. It is difficult to determine whether these 



