RADIATION AND FERTILIZING POWER. 



479 



(Curve C) to ^ l6 per cent, the increase in rate of loss of fertilizing 

 power is immediate. 



A study of Fig. 2 reveals the fact that it takes longer to reduce 

 the fertilizing power below 50 per cent, in normal sperm sus- 

 pensions than in radiated suspensions of comparable dilution; 

 that more time is needed to bring about a 50 per cent, reduction 

 in the less dilute suspensions; and that when normal eggs are 

 fertilized by dilute radiated sperm (| 12 per cent, to | 14 per cent.), 

 less than 50 per cent, cleavage follows; and finally that when 

 sperm dilutions reach | 15 per cent, to | 16 per cent., less than 10 

 per cent, of the eggs cleave. (See Table II.) The figures 

 indicate the number of minutes, following initial dilution and 

 exposure of sperm suspensions, required to reduce cleavage 50 

 per cent, and 90 per cent. It will be seen that less time is 

 required in dilute suspensions, indicating that they are more 

 susceptible to radiation effects. 



TABLE II. 



THE EFFECT OF RADIATION OF SPERM ON THE PERCENTAGE OF 

 CLEAVAGE OF NORMAL EGGS. 



That cleavage is retarded and abnormally modified by the 

 radiation of sperm, and that the length of time elapsed after 

 dilution determines the severity of the effect, even in non- 

 radiated suspensions, is clearly shown. When sperm in the 

 concentration of | n per cent, is radiated for 5 minutes and is 

 then used at intervals to fertilize normal eggs, no larvae are 

 formed, and cleavage is abortive and reduced 90 per cent, or 

 more. Table III. shows such a series for normal and radiated 

 sperm in like concentrations. 



1 Time in minutes, following dilution, required to bring the sperm into a state 

 at which 50 or 90 per cent, of the eggs fail to cleave. 



Figures 8-16 represent sperm dilutions of s 8 -3 16 per cent. 



