212 APPLIED BACTERIOLOGY 



Occurrence and Distribution. — The disease is scattered 

 throughout Europe, but is more prevalent in the northern 

 portions, and rarer in Asia. Epidemics occur at intervals, 

 exhibiting a remarkably regular quinquennial recurrence. 

 In epidemics the mortality is generally low — namely, about 

 3"0 per cent. — but it has on some occasions risen to 30'0 

 per cent. The mortality is greatest in October and 

 November, and least in March, while almost the precise 

 reverse is experienced in New York. 



One attack is usually protective. The mortality is 

 greatest at the age of three, and above this age rapidly 

 diminishes. It is therefore wise to keep children as far 

 as possible from infection in their earlier years, as later 

 in life they are far less likely to be attacked, and the 

 case-mortality is very much less. The disease requires 

 very strict sanitary control, on account of the long period 

 of infectiveness, and the readiness with which the in- 

 fective material (desquamating epidermis) may adhere to 

 clothing, etc. 



No definite relation has yet been traced between the 

 prevalence of the disease and the rise and fall of the 

 ground-water, or any other meteorological condition. 



The disease is probably conveyed chiefly by fomites, and 

 the breath, sputa, and excreta of patients should be con- 

 sidered as infective. No doubt the chief danger lies in the 

 dissemination of the disease by the desquamating particles 

 of skin. In the case of the Hendon outbreak, the disease 

 appears to have been conveyed by milk ; but the matter is 

 one on which authorities differ. There is no evidence of 

 the disease having been at any time water-borne, nor is it 

 air-borne to any considerable extent, so that hospitals need 

 not be considered as a source of danger to the surrounding 

 neighbourhood. 



Pathogenesis. — The incubation period is from about two 



