EFFECT OF RADIUM ON CELL DIVISION 201 



which contained 50 mg. of pure bromide, equivalent to 23.4 

 mg. of element. The control eggs were placed in a watchglass 

 beside the others but separated from them by a thick sheet of 

 lead. Frequent tests showed that there was no appreciable 

 difference in the temperature of the two lots of eggs during the 

 entire experiment. This point indicated that the radiations 

 from this amount of radium are not sufficient to produce any 

 marked temperature change. 



The radium tube was held in a device so arranged that the 

 tube could be held at any desired distance above the eggs. As 

 there was no screen of any kind interposed between the radium 

 and the eggs it is assumed that all of the rays emanating from 

 the tube, namely the beta and gamma rays, were able to reach 

 the eggs. After exposure the eggs, with the controls, were 

 obser\^ed almost continuously until after the first cleavage had 

 been completed. 



The amount of acceleration or retard is estimated by compar- 

 ing the time elapsing between fertilization and cleavage in the 

 controls and the radiated eggs. Thus in some experiments the 

 controls began to divide 60 minutes after insemination, and the 

 radiated eggs, in 50 minutes. The difference of 10 minutes is 

 about 16 per cent of the 60 minutes elapsing before cleavage 

 occurred in the controls. 



Exposures were made during five periods of the cell's activity, 

 namely, between 5 and 25 minutes after insemination when the 

 genu nuclei are approaching each other; second, during the 

 prophases which occur from about 25 to 35 minutes after in- 

 semination; third, during the metaphase which appears in about 

 35 to 50 minutes ; fourth, during the telophases (50 to 65 minutes 

 after insemination); and finally during the resting stages fol- 

 lowing the first cleavage. Naturally the temperature of the 

 air hastened or retarded this rate, so that in some instances 

 the exposures had to be shorter than the limits mentioned. 

 In each experiment the distance between the radium and the 

 eggs was varied from f inch to 2| inches. 



