204 CHARLES PACKARD 



Radium placed f inch above eggs 



Length of exposure Result 



5 minutes No change 



10 minutes 5 per cent retard 



15 minutes 5 per cent retard 



Radium placed | inch above eggs 



10 minutes Slight acceleration 



15 minutes 5 per cent acceleration 



At the greater distances there was no clear evidence of any 

 change. These results indicate that eggs during the telophase 

 are not as responsive as they are during the metaphase, but are 

 more like the eggs in the prophase of mitosis. 



5. Exposures made during the resting stage of the nuclei 

 were followed by no decisive changes unless the radiation was 

 intense and prolonged, in which case the eggs developed abnor- 

 mally, as would be expected. The responsiveness of the egg 

 has now reached its minimum. This result agrees very well 

 with the results of exposures made on tissues in which little cell 

 division is taking place. Unless the cells are dividing rapidly 

 radiation produces little result except when it is very intense. 



In all of these experiments it is assumed that each egg re- 

 ceives an equal amount of radiation. Probably this is not 

 strictly true, especially when the distance through which the 

 radiations pass is small, for the distance from the tube to "the 

 eggs directly under it was somewhat less than the distance to 

 the eggs further from the center of the watch glass. The fact 

 that the source of radiation is not a single point but a tube 1 cm. 

 long would also make a difference. However the inequality 

 in the amount of radiation received by the eggs is verj^ small 

 and is constant for each experiment, so the results are not 

 obscured. 



The amount of radiation which falls on the eggs decreases 

 inversely with the square of the distance through which it passes. 

 Thus if we consider f inch as a unit distance, the energy recevied 

 at f inch is one-fourth of that received at unit distance. At 

 If inches it is one-sixteenth, and at 2| inches, one thirty-sixth 

 of the unit amount. Theoretically we should expect the re- 



