ALPHA PARTICLES 565 



of corpuscles; (6) irradiation with 2.4 or 3.3 mg. RaBr2 through mica 

 screens. Estimates of the number of alpha particles necessary to 

 hemolyze a corpuscle gave the figure 2000 when radon was in solution 

 and 8000 when the rays had to penetrate through mica. 



Experiments with leucocytes showed that these had a tendency to 

 avoid or to migrate away from a region undergoing alpha irradiation. 

 Since the serum showed a decrease in surface tension when irradiated, the 

 behavior of the leucocytes was ascribed to this physical change in their 

 medium. 



These authors report general negative results when the alpha rays 

 were screened off, only the beta and gamma rays remaining effective. 

 However, they used under these conditions exposures of the same order 

 of duration as those used with all three types of rays effective. If they 

 had irradiated for longer periods, the beta and gamma rays alone would 

 probably have produced similar effects. 



Redfield and Bright (17), as a matter of fact, demonstrated this to be 

 true. They found that 25 per cent hemolysis of sheep red corpuscles 

 could be produced in 5 hr. by 0.46 mc. of radon in solution or by 54.0 mc. 

 in a glass tube (alpha rays screened off). This is another illustration of 

 the relatively enormous destructive power of the alpha particle. Hemo- 

 chromolysis and stromatolysis were found to proceed at different rates, 

 the former being complete when the latter was only about 50 per cent 

 complete. 



Swann and del Rosario (23) produced nonmotility in Euglena by 

 means of radon in solution. When the percentage of survivors was 

 plotted over time of exposure, the resulting curves were logarithmic and 

 their slopes were proportional to the concentration of radon. (The 

 effects of alpha particles from radium A and radium 'C were not con- 

 sidered.) From this result the authors concluded that the effect upon a 

 cell was due to a collision of a single alpha particle with some especially 

 sensitive volume in the cell. The calculated surface of this sensitive 

 volume corresponded to that of a sphere 4.8 /u in diameter, which is very 

 nearly the diameter of the Euglena nucleus. However, when correction 

 is made for a numerical error due to a misinterpretation of the tables 

 used, it is found that the diameter of the hypothetical sensitive volume 

 must be of a considerably lower order than that originally calculated.'^ 



Lethal effects of alpha particles upon yeast have been described in 

 papers by Holweck (10), and by Lacassagne (12), and by these two 

 authors jointly (11). Two types of effect were classified: (a) no cell 

 division ("immediate death"); (6) one cell division ("deferred death"). 

 Cells accomplishing more than one division were considered miaffected. 

 Dosage was calculated in terms of number of ion pairs produced per 



' The value and validity of the concept of a "sensitive volume" have been dis- 

 cussed by Crowther (3). 



