1905 - 6 .] Studies in Immunity : Theory of an Epidemic. 505 
that the loss of infectivity has been specially rapid ; and though 
a large amount of infection has been thrown into the milk, yet 
when it is observed that the incubation period of scarlet fever is 
from three to five days, it can be seen that at the time the 
milk supply was stopped, the organism had in both instances run 
almost the complete cycle of its infectivity. The germ, therefore, 
of scarlet fever, though it can possibly be introduced into eruptions 
on the teats of cows, yet cannot evidently long maintain its 
infectivity if growing in that situation. When a milk supplied 
from such infected animals has been distributed in a new centre 
Diagram XXI. 
-200 
— 
\ 
Enteric 
Maidstor 
: Fever 1 
ie. 
nearly III. 
Didemic. 
Cases. 
-100 
/ 
''' 
Type 1., i 
Water E| 
/ 
/ 
Sept 5 Sept 8 Sept 11 Sep 
! 1 
1 14 Sept 19 Sep' 
t20 Sept23 Se 
pt26Sept29 0 
1 1 
ct2 Oct 5 O 
ct8 Oct 11 Od 
1 14 Oct 17 Oc 
't 20 Oct 23 
after the outburst of disease has led to its discontinuance in the 
infected area, though a few cases of fever might occur among the 
new customers, no outbreak comparable to the original one has 
been observed. Here a comparison may be made between the 
milk epidemic at Wimbledon and that previously referred to as 
occurring naturally at Halifax. Both curves have much the same 
