338 A. J. S. DAVIES, ANNE M. CROSS, AND P. C. ROLLER 



not know why, but this of course makes quite a difference to this sort of analysis. I 

 wonder if I could ask Prof. Koller or Dr. Davies whether they have in fact observed 

 considerable systematic alteration in the absolute numbers of counts in their controls. 

 davies: We have not observed any seasonal variation. The variation which has been 

 observed has been taken into consideration using standard statistical methods. 



