382 DISEASES OF CATTLE. 



A Avide distribution of the virus and a rapid infection of a herd is 

 the result. Animals may be infected directly, as by licking, and in 

 calves hj sucking, or indirectly by such things as infected manure, 

 hay, utensils, drinking troughs, railway cars, animal markets, barn- 

 yards, and pastures. Human beings may carry the virus on their 

 shoes and clothing and transmit it on their hands Avhen milking, since 

 the udder is occasionally the seat of the eruption. It may also be 

 carried by dogs, cats, rats, chickens, pigeons, etc. Milk in a raw 

 state ma}'^ also transmit the disease to animals fed with it. 



The observations made by some veterinarians would lead us to 

 suppose that the virus is quite readily destroyed. It is claimed that 

 stables thoroughly cleaned become safe after drying for a short time ; 

 hence, litter of all kinds, such as manure or soiled hay and straw, may 

 remain infective for a longer time because they do not dry out. 

 Other authorities maintain that the virus is quite tenacious and may 

 live in stables even so long as a year. They also state that animals 

 which have passed through the disease may be a source of infection 

 for several months after recovery. 



Unlike most other infectious diseases, foot-and-mouth disease 

 may repeatedly attack the same animals. The immunity conferred 

 by an attack is of limited duration. 



The period of incubation (that is, the time between the exposure 

 of an animal to infection and the development of the disease) is 

 variable, usually from three to six days. The disease maj ajjpear 

 in '24: hours, or, in exceptional cases, not for 18 days or even longer. 



Losses. — The highly contagious character of foot-and-mouth dis- 

 ease and its rapid spread to practically all exposed susceptible ani- 

 mals lead to heavy losses. Since the mortality is comparatively low, 

 ranging from only 3 per cent or less in mild forms to 30 or 40 per cent 

 in malignant cases, the havoc caused by the pestilence is sometimes 

 underestimated. But there are other sources of loss which are much 

 more important than the actual mortality. The fever and the 

 difficult}^ of eating cause a rapid and extreme loss in flesh and a 

 lessening or cessation of the milk secretion. The udders often 

 become inflamed and ruined by the formation of abscesses, and cows 

 affected in this way are sometimes rendered permanently valueless for 

 milk production. The inflammation of the feet may cause the horn 

 to drop from the toes, producing great lameness and lasting injury. 

 Abortion is frequent, and typical lesions have been observed in the 

 newly born at birth. Altogether these losses may amount to 20 or 

 30 per cent of the value of the affected animals. 



In addition there are indirect losses of a commercial nature. 

 Dairy farmers are put out of business for a time. Necessary quar- 

 antine restrictions greatly interfere with the movement of live stock 

 and such commodities as hay, straw, hides, and farm produce. The 



