RADIATION AND FERTILIZING POWER. 475 



Method. In these experiments, measured dilutions of sperm 

 (i per cent, to 1/240 per cent.) were exposed, as a thin film just 

 covering the bottom of the dish, to radiation from a Cooper 

 Hewitt quartz mercury-vapor arc at a distance of 30 cm. for one 

 minute. (Temperature was controlled by means of a water 

 bath. No attempt was made to screen out visible or other rays 

 from the spectrum of the arc.) Dilutions of sperm were made 

 after the manner of F. R. Lillie, '156, on a percentage basis, 

 using as "stock" the thick fresh sperm as it exuded from the 

 genital pore of cut, inverted Arbacia males. 



Immediately after exposure, samples of one drop each of 

 radiated and nonradiated sperm of the same dilution, were 

 transferred to dishes containing 10 cc. (300 drops) 1 of a known 

 concentration of eggs in sea water (3-5 per cent, in these experi- 

 ments). In drawing off samples of radiated sperm, care was 

 taken to obtain sperm from the upper surface at the center of 

 the dish. At short intervals thereafter, up to three hours, 

 samples of radiated and nonradiated sperm, kept under similar 

 conditions, were used to fertilize normal eggs. At the end of 4 

 or 5 hours, the percentage of eggs which had formed membranes 

 and of those which had cleaved was determined on the basis of 

 a count of 200 eggs in each case. 



By comparing results obtained following ultraviolet radiation, 

 with those obtained from normal lots of eggs it was possible to 

 estimate the degree to which radiation had inhibited the fertilizing 

 power of a given dilution of sperm. 



Results. -It was found that in normal sperm suspensions, 

 fertilizing power decreased as time after removal of the first 

 sample increased; the more dilute the sperm suspension, the 

 more rapid was the rate of decrease. (See also F. R. Lillie, '156.) 

 Time and dilution, then, are factors in determining the fertilizing 

 power of normal sperm. (See Table I.) 



Exposure of dilute sperm to ultraviolet radiation augments the 

 rate of loss of fertilizing power beyond that following dilution 

 alone. Fewer eggs cleave (see Table I.), or even form mem- 



1 Sperm was thus further diluted 300 times. Concentrations of sperm at the 

 time of insemination were therefore 1/300 per cent, to 1/72,000 per cent., (^ 8 per 

 cent, to 5 16 per cent.) 



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