INFECTIOUS DISEASES OF CATTLE. 397 



Estimating the losses upon the surviving animals from this basis 

 and adding the value of those that die, it will be seen that an outbreak 

 of this disease may quickly result in direct losses of many millions of 

 dollars. In addition to this, a considerable spread of the contagion 

 in this country would entail the entire loss of our export trade in live 

 animals, interruptions of domestic commerce, and quarantines, which 

 would surpass the loss caused by the ravages of the disease. 



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

 attack the same animals repeatedly. The immunity or protection 

 conferred is thus only of limited duration. Hence protective inoc- 

 ulation with the virus, in whatever manner it may be practiced, 

 is not only of no use, but decidedly dangerous, as it will introduce the 

 disease. It is, however, not uncommon in European countries to 

 practice inoculation after the disease has appeared in a herd in order 

 to hasten its progress. This is highly recommended by some, since 

 it not only hastens the infection, but the disease is apt to be milder 

 and limited to the mouth. It consists in rubbing with the finger or a 

 piece of cloth a little of the mucus from the mouth of a diseased ani- 

 mal upon the inner surface of the upper lip of those to be inocuhited. 

 From 50 to 75 per cent of the inoculated animals take the disease. 



Cause. — As with other communicable diseases, the source and ori- 

 gin of foot-and-mouth disease have given rise to much si>ecuhition. 

 The disease had been known in Eurojx" for centuries, but it was not 

 until a comparatively recent date that the erroneous conceptions of 

 its spontaneous origin as a result of climatic and meteorological con- 

 ditions, exhausting journeys, etc., were abandoned. It is now con- 

 ceded that foot-and-mouth disease is propagated by a specific virus 

 and that every outbreak starts from some preexisting outbreak. 



The causative agent of this disease has not been isolated, although 

 nmnerous attempts have been made to cultivate and stain it. Experi- 

 ments have shown that the virus will pass through standard srerm- 

 proof filters, thus indicating its minute size and the reason it has not 

 been detected by the staining methods. The contagion may be found 

 in the serum of the vesicles on the mouth, feet, and udder; in the 

 saliva, milk, and various secretions and excretions; also in the blood 

 during the rise of temperature. 



A wide 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 by sucking, or indirectly by fomites. such as infected manure, 

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

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

 clothing and transmit it on their hands when milking, since the udder 

 is occasionally the seat of the eruption. Milk in a raw state may also 

 transmit the disease to animals fed with it. 



