lotka: contribution to epidemioIvOgy 73 



Nummulites characterizing the Claiborne occurs just below the 

 Ocala and makes an excellent criterion for delimiting that forma- 

 tion. The Ocala also dips to the northeastward and to the 

 south from the Apopka region. 



From the present occurrence of the Ocala above sea level in 

 west central Florida and its occurrence in the Tiger Bay and St. 

 Augustine wells at 360 and 224 feet, respectively, below the 

 surface, a dip somewhat like that of the Lower Cretaceous is 

 indicated. 



The general conclusion from the evidence of the Foraminifera 

 is that the whole of the Florida peninsula and probably a part 

 of north Florida as well, as indicated from the data near Burns, 

 are underlain by rocks of Lower Cretaceous and perhaps older 

 age and that on the Lower Cretaceous the upper Eocene beds 

 were deposited. The area was probably uplifted at the end 

 of the Lower Cretaceous and remained a land mass during 

 Upper Cretaceous and early Eocene time, after which it was 

 again depressed and except in the region of Apopka was under 

 water during the deposition of the Ocala Umestone in late Eocene 

 time. 



Epidemiology. — a contribution to quantitative epidemiology. 

 Alfred J. Lotka, New York City. 



In his recent paper on Pathometry^ vSir Ronald Ross de- 

 velops, for a certain class of cases, the equation 



F,,o = A/P J" c F,s ds. (i) 



In this equation Ff^ ds denotes the number of cases which 

 at time t have been afifected for a length of time comprised within 

 the limits of 5 and 5 + ds; Fio is accordingly the rate at which 

 new cases are developed at time t. The total population is P, 

 the unaffected population A, while c is the coefficient of in- 

 fectivity. 



A solution is given by Sir Ronald Ross, among other things, 

 for the special case that the coefficient of infectivity c is inde- 



1 Proc. Roy. Soc. 93: 235. 



