EFFECT OF X-RAYS ON RATE OF CELL DIVISION. 9 1 



"The broadest, and at the same time the most definite general- 

 ization warranted by the work so far done is that the rays of 

 radium act as a stimulus to metabolism. If this stimulus ranges 

 between minimum and optimum points, all metabolic activities, 

 whether constructive or destructive, are accelerated; but if the 

 stimulus increases from the optimum toward the maximum point 

 it becomes an over-stimulus, and all metabolic activities are 

 depressed and finally completely inhibited. Beyond a certain 

 point of over-stimulus recovery is impossible, and death results." 



Another statement of the same fact is given on page 157: 

 'The rays of radium act as a stimulus to protoplasm. Retarda- 

 tion of growth following exposure to the rays is an expression of 

 over-stimulation, acceleration of growth indicates stimulation 

 between a minimum and an optimum point." 



Protozoa present some variation in their reaction to X-rays. 

 Some are killed but others are very resistant and appear little 

 disturbed. Some are much more susceptible than others. In 

 some cases cytoplasmic and nuclear activities are affected, while 

 in other cases such a process as conjugation goes on apparently 

 unaffected. There is no positive evidence of tropic responses to 

 radiations. Bardeen reports that Paramcccium may be exposed 

 as much as twelve hours without disturbing conjugation, or the 

 rate or forms of division. 



The effect of radium upon Ascaris eggs has been studied by 

 Perthes, by Barlow and Bonney, and by Paula Hertwig. The 

 former found that after exposure the cell divisions became slower 

 and more irregular than the control, and finally gave rise to 

 irregular cell masses or misshapen little worms especially abnormal 

 at the posterior end. The controls, however, gave rise uniformly 

 to active worms. The eggs in the resting and dividing conditions 

 were equally affected, and the degree of exposure is the factor 

 upon which the result depends. Nuclei and in particular the 

 chromatic structures were most injured, while spindle and centro- 

 somes appeared quite normal. The chief effects did not appear 

 at once upon stimulation but only after a certain period of time 

 had elapsed. The results obtained from X-rays were entirely 

 analogous to those from radium. 



Barlow and Bonney, studying "the influence of radio-activity 



