28 PHYSIOLOGICAL EFFECTS OF /3- AND 7-RAYS 



of these rays and their consequent absorption coefficients are not 

 uniform. The following values may be assigned to the absorption 

 coefficients of these rays/ 



Substance. 

 Radium B 



In contrast to these figures the absorption coefficient of the 7-rays 

 is of a smaller order, being 0.111 according to Soddy and Russell.^ 

 The dotted Line in Fig. 1 indicates how little the filters used would 

 cut down the intensity of rays with this coefficient of absorption. 

 If the absorption coefficient, fj, = 23.9 cm.~\ for the physiologically 

 effective radiation is compared with these values it is obvious that 

 this figure is of the order of magnitude of the absorption coefficient of 

 /3-rays. We conclude, therefore, that the /S-rays constitute the physi- 

 ologically effective radiation and that the influence of the 7-rays 

 on this reaction is negligible. This result is quite in accordance 

 with expectation, for a number of investigations have indicated that 

 the physiological effects of radiations of different types are roughly 

 proportional to the ionizing powers of the rays involved.^ The 

 ionizing power of the 7-rays is probably about only 1 per cent of that 

 of the /S-rays. 



In order to determine whether the 7-rays have any effect on the 

 volume of the fertilization membrane of the Nereis egg a lot of eggs 

 was exposed for 11.5 hours to an intensity of radiation of 65 milli- 

 curie centimeters filtered through 1.9 mm. of lead and 1.7 mm. of 

 cardboard. This thickness of lead completely absorbs the primary 

 iS-radiation while the cardboard stops the slow electrons sent out 

 from the lead by the 7-rays. The membranes of eggs treated in 

 this way had an average volume of 5.9 X 10^ cubic microns, while 



' Rutherford, E., Radioactive substances and their radiations, Cambridge, 

 1913,225. 



8 Soddy, F., and Russell, A. S., Phil. Mag., 1909, xviii, 620. 



®Russ, S., Arch. Middlesex Hospital, 1912, xxvii, 16. Lazarus-Barlow, W. S., 

 and Beckton, H., ibid., 1913, xxx, 47. 



