CONTAGIUM 79 



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 recur 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. 

 A widespread outbreak of anthrax occurred in France and Bel- 

 gium, 591 A. D. This same disease is said to have spread all 

 over Europe again about 1750. Cattle plague was carried into 

 England in 1745, and the loss was very heavy. This outbreak 

 lasted for several years in various parts of Europe, and the loss 

 cannot be estimated. Tuberculosis has long been prevalent. 

 These are all contagious diseases and are caused by bacteria. 

 The above are but isolated examples of an indefinite number of 

 outbreaks of various diseases which have appeared among do- 

 mestic 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 the diseased carcasses, hog racks, stock 

 cars, and they may be easily transferred by the shoes or clothing 

 of persons who walk through an infected yard. Dogs undoubt- 

 edly serve to scatter this disease over wide areas, and possibly 

 birds. It is possible, also, for the germs to be scattered upon 

 particles of dust and litter in high winds. Watering troughs, 

 tanks, ponds and sluggish streams are all common sources for 

 spreading infectious diseases. 



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

 and possibly so of a great many diseases, that the germs may be 

 present with the animal or his surroundings but not virulent 

 enough to produce disease. Under favorable conditions and per- 

 haps after passing through the bodies of several susceptibk ani- 

 mals in succession they may increase in virulence sufficently to 

 produce disease. 



Some of the germs producing diseases of domestic animals 

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

 even vegetate outside the animal body, possibly upon or within 

 the tissues of plants. Some germs, especially in the resisting or 

 spore stage, may live for very long periods of time, and under very 



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