INFECTIOUS DISEASES OF CATTLE. 383 



removed or disinfected. In every one of these cases the destruction 

 of the stable, the burning of the hnnber of which it was constructed, 

 the removal of the accumulations beneath the floors, and the thor- 

 ough disinfection prevented the recuiTence of the plague in new 

 stables built vipon the same premises. This experience conclusively 

 shows that under certain conditions, at least, stables may retain the 

 infection for a considerable time, and that when restocked the disease 

 may break out again from such infection. 



As a rule, however, the disease is acquired by a healthy animal 

 being near to an affected one and receiving the contagion direct. 

 Affected animals may give off the contagion in the early stages of the 

 disease before the symptoms are apparent to the observer, and they 

 may retain this infectious character, if they survive the attack, for 

 six months and probably for a year after all symptoms of the disease 

 have disappeared. 



Incubation. — The time which elapses between exposure to the con- 

 tagion of pleuropneumonia and the first appearance of the symptoms 

 of this disease varies greatly with different individuals and with dif- 

 ferent outbreaks of the disease. Ordinarily the symptoms of disease 

 make their appearance within three to six weeks after exposure ; 

 but they may be observed within two weeks or they may not become 

 apparent until nearly or quite three months. It is this long period of 

 incubation and the great length of time that an animal may dissemi- 

 nate the contagion after apparent recovery which give the plague 

 that insidious character so often spoken of, and which greatly in- 

 crease the difficulties of eradication. 



Symptonis, — The symptoms are such as would be expected with 

 inflammation of the lungs and pleurae, but they vary considerably 

 according to the type which the disease manifests. If the attack is 

 an acute one, as is frequently seen in hot weather, the symptoms 

 appear suddenly ; the breathing becomes rapid and difficult, the ani- 

 mal grunts or moans with each expiration, the shoulders stand out 

 from the chest, the head is extended on the neck, the back is arched, 

 the temperature is 104° to 107° F., the milk secretion is suspended, 

 there is no appetite, rumination is stopj^ed, the animal may bloat and 

 later be affected with a severe diarrhea. Such cases are generally 

 fatal in 7 to 20 days. 



Very often the attack comes on slowly and the symptoms are much 

 less clear. In the mildest cases fthere is a cough for a week or two, 

 but no appreciable loss of appetite or elevation of temperature. The 

 lungs are but slightly affected and recovery soon follows. Such 

 animals may disseminate the contagion for a long time without being 

 suspected, and for that reason are the most dangerous of all. 



A more severe type of the plague is the most frequently seen. In 

 these cases the cough is frequent, more or less painful, the back 



