566 



BIOLOGICAL EFFECTS OF RADIATION 



cubic micron. The doses necessary to produce deferred death and imme- 

 diate death in 50 per cent of the cells (observations made 24 hr. after 

 irradiation) are tabulated below. The results of similar calculations 

 for soft X-rays are shown for comparison. 



Radiation 



Alpha 



X (1.93 A) 

 X (8.32 A) 



Ion pairs per cubic micron 

 necessary to produce: 



50 per cent 



deferred 



death 



58,000 

 47,000 

 30,000 



50 per cent 



immediate 



death 



810,000 

 750,000 

 600,000 



These results indicate that the amount of ionization necessary to 

 produce a given degree of effect is of the same order for all of these 

 radiations. 



Feichtinger (5) made comparative studies of the effects of alpha rays 

 (from polonium) and beta rays (from radium C and radium E) upon the 

 root-tip cells of Crepis virens. Her sources of alpha and beta rays were 

 estimated to be of equivalent ionizing power per unit volume of proto- 

 plasm. After irradiation the roots were fixed, embedded, sectioned, and 

 stained with iron-alum hematoxylin. Three stages of effects were 

 recognized: (a) increased affinity of the cell contents for the stain; (6) 

 formation of vacuoles and clumping of protoplasm, the cell as a whole 

 appearing deeply stained; (c) breaking up of the protoplasm into small, 

 deeply staining granules which lie near the cell wall, the cell as a whole 

 appearing rather empty. For equal estimated ionization per unit 

 volume, the effects of the alpha and beta rays were the same. The 

 alpha-ray effect was limited to an external layer about 30 /x thick, while 

 the beta rays were effective in all cells of the root. This, of course, was 

 to be expected because of the difference in the penetrating powers of the 

 two types of radiation. 



In a recent paper (6) the same author reports viscosity changes in 

 cells of Spirogyra irradiated with alpha particles. As the dosage was 

 increased, the viscosity (as indicated by migration of chloroplasts under 

 centrifugation) first decreased and then increased. Beta rays had a 

 similar effect. These results appear in agreement with the observations 

 of Williams (26) that X-rays first increase and then decrease the rate of 

 protoplasmic streaming in various plant cells. 



The low and nearly uniform penetration of polonium alpha particles 

 makes it possible to irradiate limited portions of cells ranging in diameter 



