250 



BIOLOGICAL EFFECTS OF RADIATION 



time proceeds at a rate represented by B (0.993). Thus the eggs recover 

 as to their cleavage time at a rate of 0.7 per cent per min. of delay in 

 insemination. This rate of recovery in cleavage time with increasing 

 delay of insemination is constant for various degrees of exposure. 



Having derived any equational relationship between two variables, 

 such as the ones just discussed, we naturally want some measure of the 

 accuracy with which the equations represent the observed facts. The 

 variability of the observed points about the curve is usually measured in 



to 20 30 40 50 bO 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220 

 Interval From Irradiation to Insemination tMinutes) 



Fig. 6. — Recovery of Arbacia eggs from the effect of roentgen rays on their cleavage time. 



terms of a standard deviation which we shall represent by the symbol 

 (Ty. X. This standard deviation is obtained by calculating from the equation 

 a y value for each point on the x scale where an observation has been 

 made, and then following the equation 



^y.x — y\ 



S(l/ob6 — Vc^cY 



n — a 



where n is the number of points to which the equation has been fitted and 

 a represents the number of derived constants. This standard deviation 

 may be used in connection with Table 3 to determine the extent of the 

 variation between the observed and calculated values. It is also the basis 

 for the computation of the degree of sampling variation of the derived 

 constants of the equation. 



The methods outlined in this paper are characteristic of statistical 

 treatment as a whole, and although they may seem varied in type, they 



