EFFECTS OF RAYS OF RADIUM ON PROTOPLASM 325 



Abbe ('14) exposed wheat grains to mixed beta and gamma 

 rays for varying periods and at varying distances. "The uni- 

 versal effect was a depression of growth exactly in proportion 

 to both time and distance. The greatest destruction of seed 

 life was at one inch." In no instances was there any evidence 

 of an acceleration in the rate of growth. Carrel (quoted in 

 Abbe's paper) found that the gamma rays produce no effect 

 on the rate of cell growth in vitro but that the beta rays bring 

 about a retardation of 25 to 50 per cent. There was no morpho- 

 logical change in the cells. The effect of a short radiation per- 

 sisted through twenty cell generations. 



Experiments in which there has been no attempt to differenti- 

 ate between the action of the different kinds of radiation have 

 been numerous. I will not attempt to review them here for 

 they have been mentioned in a previous paper and by Hertwig 

 ('10) and Richards ('14). The point which is of interest in con- 

 nection vv'ith the present study is that a strong radiation retards 

 development and may produce many abnormalities. A very 

 weak and short exposure brings about an acceleration (Cong- 

 don '12). Between these extremes it is possible to radiate 

 developing embryos so that no abnormality results although 

 there is a- marked retardation. 



METHODS 



The beta rays can be separated from the gamma rays in a 

 magnetic field, since the former are deviable and the latter are 

 not. The device for separating the rays is shown in text figure A. 

 The block is made of solid lead. The capsule containing the 

 radium (50 mg. of the pure bromide) rests in the chamber A, 

 the bottom of which consists of a sheet of lead 2 mm. in thickness. 

 This is sufficient to absorb all of the beta rays projected down- 

 wards on the shelf B. Thus only gamma rays can fall on material 

 placed in that position. When the device is placed between 

 the poles of a strong electromagnet the beta rays are deflected 

 in the manner indicated and fall upon material placed on the 

 shelf C. The path of the rays, which under these conditions 



