1905-6.] Studies in Immunity : Theory of an Epidemic. 487 
of emigrants began in great numbers. On this Pepys makes 
anxious remarks in his Diary, and speculates on the occurrence of a 
recrudescence of the malady, but the infecting power of the 
organism was exhausted ; and though great numbers of susceptible 
persons came from the country into the zone of infection, even, it 
is said, occupying the beds of those who had been afflicted, no 
further extension of the disease ensued. The curve of this 
epidemic is given in diagram II. The figures on which it is based 
are taken partly from the London Bills of Mortality * and partly 
from Pepys’ Diary. For comparison, the constants of the curve 
representing the course of the great outbreak of plague in London 
in 1563 f are given. 
As further examples of the epidemic course, influenza j and 
cholera (Table A, Nos. 4, 5, 6, and 7) are illustrated (diagrams 
III., IV., and V.), and the constants given in the table. It is to be 
noted that the curves are again of the type IV. The epidemics 
of cholera include that in Exeter in the summer of 1832,§ and 
* Quoted also in Creighton’s History of Epidemics in Britain , vol. ii. 
f Loc. cit vol. i. p. 305. 
7 Reports of Registrar- General for England. 
§ History of Cholera in Exeter in 1832, Shapter, p. 208. 
