SOURCES OF INFECTION 57 
mental inoculation and infection by cohabitation, the 
date of exposure to infection being known in every case, 
and the consensus of opinion computes the average 
period at 4 to 7 days. The earliest appearance of 
symptoms has been placed at 3 days, and the longest at 
3 weeks (Hobday), whilst many other authorities have 
recorded intervening periods, such as 5 to 8 days 
(Trasbot), 12 to 15 days (Nocard and Leclainche). 
Krajewski found the period of incubation was 4 to 
7 days, but he states that cases of infection through 
cohabitation may sometimes take from 2 to 24 weeks to 
develop. These protracted periods, however, are rare, 
and personally I would expect to discover the earliest 
symptom about a week after a susceptible dog had been 
exposed to the disease. 
