THE FACTOR OF IMMUNIZATION 



191 



Strain combination. The best approximation we can get is, there- 

 fore, the "semi-platonic" slope which is determined by pooling 

 all top dose indices from the 2 sets of data and subtracting the 



Spken 

 Index 



3.00 



2.50 



2.00- 



I.50 



1.00 



CgH-^CgH X ST/A 



I09. Dose 



pool of bottom dose indices, and dividing the result by 2 times 

 the number of test litters multiplied by the dose range (which is 

 log 9 in both curves). Therefore the formula for the slope is: 



Sk + SNs-jSI^+SN^) ^ 



2X I2X log 9 



b equals in this experiment 1-32. 



