476 BIOLOGICAL EFFECTS OF RADIATION 



injured which are able to recover completely in function and reproductive 

 power. All variations between acute fatal injury and return to normal 

 are relative to dosage and sensitivity. 



In every organ there are probably a few cells in such a stage of "sensi- 

 tivity" that a certain minimal dosage of radiation will be lethal for them. 

 There are also, in even the more sensitive cell groups, some cells which 

 will survive extremely large doses of radiation which will have killed all 

 of the other cells of a given organ. These few cells, some of them abnor- 

 mal now, attempt to regenerate, and the degree of success in restoring 

 the function of the organ involved is determined, to a great extent, by the 

 number of functioning survivors and the defects brought about by 

 the collapse of the destroyed cells. Lack of knowledge of many of the 

 intimate processes going on within the cell is, of course, a handicap com- 

 mon to the whole field. The investigator may very well apply the 

 methods used with the simpler biological materials (see other papers in 

 this work) to experiments dealing with the more complex organs in 

 animals. 



A study of the time relations of some of these effects of irradiation 

 must be divided up into two considerations: first, the immediate death 

 of a certain number of the cells following irradiation, and the repair or 

 failure of repair of this damaged area, and second, the prolonged degenera- 

 tive processes in cells not killed and the resultant disturbances therefrom. 

 A true "latent period," therefore, should, strictly speaking, involve only 

 the acute injury, including death, of the cell, and occupy that time 

 interval between the irradiation and the disturbance in function of the 

 particular type of cell under investigation. Since the cells in a given 

 organ are apt to vary somewhat in their sensitivity at the time of any 

 given irradiation, one may have all stages of injury of the cells in an organ 

 from minimal injury to death. This will be evidenced as an average 

 effect of the total damage done and will influence the functional dis- 

 turbance and histological and gross appearance of the organ accordingly. 



In considering the effects of radiation upon the organ systems and in 

 particular the efi"ect of roentgen and radium radiation, it is necessary 

 to take into consideration the methods of dosage as well as the total 

 amount involved and the time interval between various doses. There 

 are three main types of dosage: first, the "massive-dose" method, in 

 which the total, usually near the erythema dose, is given at one sitting 

 within a short or relatively prolonged period of time, usually depending 

 upon the amount of energy available to the investigator; second, the 

 ''fractional method" in which a definite proportion of an erythema dose 

 is given at regular short intervals, either as a dose of high intensity given 

 over a short period of time, simple fractional method, or the same dosage 

 of radiation given with low intensity over a relatively long period of time, 

 protracted fractional method ; third, the method of giving a large dose of 



