CONTAGIUM 97 



Plagnes in history. — Throughout all the pages of history, we 

 have records of fearful plagues among men and animals. About 

 fifteen hundred years before Christ a great plague of animals 

 swept through Egypt and made a great slaughter of cattle. We 

 are told concerning the plague at Athens, 430 b.c, that dead 

 men, dead animals, and dead birds lay in piles on the streets, 

 and even the temple floors were covered with bodies. 



Plagues recurred at intervals through the history of the city of 

 Rome. About 453 b.c. an outbreak, possibly anthrax, destroyed 

 nearly one half the population of Rome, as well as their cattle, 

 and the outbreak spread extensively through what is now Italy. 

 Cattle plague was carried into England in 1745, with heavy loss. 

 This outbreak lasted for several years in various parts of 

 Europe, and the loss cannot be estimated. Within present 

 memory have come several enormously expensive outbreaks oi 

 hog cholera and foot and mouth disease. Tuberculosis has long 

 been prevalent. These are all infectious diseases caused by 

 bacteria. 



The above are but isolated examples of an indefinite number 

 of outbreaks of various diseases which have appeared among 

 domestic animals. 



How scattered. — Germs of diseases are scattered by a very 

 great many agencies; for instance, the germs of hog cholera 

 are disseminated by means of sick animals, diseased carcasses, 

 hog racks, and stock cars, and they may be easily transferred 

 by the shoes or clothing of persons who walk through an in- 

 fected yard. Dogs, and possibly birds, serve to scatter this 

 disease over wide areas. Watering troughs, tanks, ponds, and 

 sluggish streams are all common sources for spreading infectious 

 diseases. Infections may be spread in any ordinary way that 

 very fine particles of dust are carried. 



Development of outbreaks. — It seems to be true of several 

 diseases tliat the germs may be present with the animal or his 

 surroundings but are not virulent enough to produce disease. 

 Under favorable conditions, and perhaps after passing through 

 the bodies of several susceptible animals in succession, they 

 may increase sufficiently in virulence to produce disease. 



Some of the germs producing diseases of domestic animals 

 are believed to live for very long periods of time and even 

 vegetate outside the animal body, possibly in the soil upon or 

 within the tissues of plants. Some germs, especially in the re- 



