DISEASES OF COWS. 433 



that a period of incubation is required for the develop- 

 ment of the disease. 



4. When by accident infected stables have been de- 

 stroyed by fire, .and with the infected herd have been 

 totally consumed, the disease has disappeared from the 

 farm. 



5= Abortion usually occurs during the fourth month, 

 although it may happen at any period of gestation. 



6. It appears to be a rale that the time of occurrence 

 of this disease arrives later in the period of gestation of 

 the infected cows in succeeding years ; thus a cow which 

 loses her calf one year in the fourth month, will not 

 abort the next year until the fifth, and the year after 

 until the sixth, and so on until the full time be passed, 

 when the calf will appear to be full grown and healthy, 

 but after a short time will be stricken with disease and 

 perish apparently of inanition and weakness. 



7. The condition of the cow does not seem to have any 

 effect upon the progress of the disease, and heifers with 

 their first calf are as likely to be affected as older cows. 



8. A cow under the influence of the infection gives no 

 indication of suffering — eats, drinks, and milks as usual. 

 But by close observation a changed appearance of the 

 visible organs is to be noticed, a looseness of the parts 

 and sinking of the muscles which always appear before 

 calving become plainly apparent, and heifers ^^ spring" 

 and exhibit the full udder as if about to calve naturally. 

 One who has become experienced in the behavior of the 

 diseased cows knows beforehand that the animal in- 

 fected is about to abort. 



9. The expulsion of the foetus is so easily and quickly 

 accomplished, and the cow shows so little concern or 

 injury, that unless the owner is forewarned the accident 

 might pass without notice, excepting when the foetal 

 membranes are retained ; these being then removed with 

 much difficulty, and on their appearance they show in- 



