560 IMMUNITY 



resulting from too strong a virus, too weak a serum, or the 

 high resistance or unusual susceptibility of the individual are 

 possible conditions to be kept in mind. 



§ 451. Prevention. The prevention of the specific dis- 

 eases of animals, when considered from the point of view of 

 etiology, is not so difficult as is often supposed. Infectious 

 diseases are simply parasitisms. If the infecting organisms 

 can be kept away from animals the diseases they would pro- 

 duce cannot appear, and if the individuals already siiffering 

 from the disease are properly isolated, their stables and pens 

 disinfected, and their bodies properly destroyed if they die, 

 the infecting organisms must perish. The great Pasteur said, 

 " It is within the power of man to make all infectious diseases 

 disappear from the world." The fact that the bacteria of 

 these diseases are parasites restricts their breeding places, so to 

 speak, to the animal body. If, therefore, the channels 

 through which these microorganisms escape from the infected 

 body are properly guarded, and if the channels through which 

 they enter the healthy body are intelligently protected, the 

 spread of infectious animal diseases will be minimized, it 

 not entirely prevented. 



Since the discovery of a specific etiology the life history 

 and possibilities of the virus of the different infectious diseases 

 have been diligently studied and much has been learned con- 

 cerning them. The result is that frequently by taking ad- 

 vantage of the present knowledge of the infecting organism, 

 preventive measures may be taken that will give equally as 

 good results as vaccine, without its dangers, and often with as 

 little trouble and expense. The prevention of these diseases 

 is well illustrated in many instances where owners of animals 

 have protected their herds against the sources of infection 

 when surrounded with widespread epizootics. Whole coun- 

 tries have been kept free from certain maladies by enjoining 

 the same methods, as shown in the absence of rabies in Aus- 

 tralia. This was accomplished by prohibiting the entrance of 

 dogs until after they had been quarantined for a sufficient time. 

 The eradication of infectious diseases by holding rigidly and 



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