416 DISEASES OF CATTIiE. 



stroyed. It is claimed that stables thoroughly cleaned 

 become safe after drying for a short time. Hence, lit- 

 ter 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 attack the same animals repeatedly. No 

 definite immunity is conferred by an attack. 



The period of incubation (that is, the time elapsing 

 between the exposure of an animal to infection and the 

 development of the disease in that animal) is variable, 

 usually from three to six days. The disease may appear 

 in 24 hours, or, in exceptional cases, not for 18 days or 

 even longer. 



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

 mouth disease and its rapid spread to practically all 

 exposed susceptible animals 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 difficulty of eating cause 

 a rapid and extreme loss in flesh and a lessening or cessa- 

 tion 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 per- 

 manently valueless for milk production. The inflamma- 

 tion of the feet may cause the horn to drop from the toes, 



