14 



E. J. LUND 



rate of food taken by the two cultures was not due to some 

 sporadic difference caused, for example, by a ver}^ high rate of 

 feeding by a few individuals and no food eaten by others, but 

 rather to a uniform difference between the sets of individuals 

 from the two cultures. Therefore the results are typical for 

 the individual as well as for the culture as a whole. Moreover, 

 if we calculated the averages of A and B on the basis of those 

 individuals alone which had one or mt)re grains, the average of 

 A would still be greatly in excess of that of B. 



20 30 60 



Fig. 2 Showing the rates of feeding by the two cultures A and B, curves A 

 and B, respectively. Plotted from the results of table 1. 



We may express the variation in the total quantity eaten by 

 the standard deviation of each corresponding group of thirty 

 individuals in A and B, as is done in the last column of table 2. 

 The reciprocal of the standard deviation (cr) is a measure of the 

 degree of uniformity among the individuals. It will be noted 

 that there is an increase in the range of variation and the stand- 

 ard deviation with increase in the length of time of feeding; this 

 means that the difference in physiological state among indi- 

 ^4duals of the same culture finds a fuller and more definite ex- 



