PREVENTION 561 



simply to the guarding of the channels of dissemination and 

 infection has been accomplished a number of times on a large 

 scale as instanced by the eradication of contagious pleuropneu- 

 monia in cattle from this country and from Great Britain. The 

 elimination of foot and mouth disease from New England is 

 another striking illustration of active decisive efforts in this 

 direction. Tht eradication of infectious diseases from individ- 

 ual herds is being accomplished repeatedly by adhering to the 

 same methods. The Bang method of handling bovine tuber- 

 culosis, as already mentioned, enables one to protect the well 

 animals and to save all there is of value in the others. 



Tlie isolation of the well from the sick and the thorough 

 disinfection of the houses and yards containing the sick has 

 resulted in stopping many outbreaks of disease. This is fol- 

 lowed very generalh^ even where vaccination and serum pre- 

 vention treatment are resorted to. Several times in the 

 writer's experience success in. checking the spread of the 

 disease by vaccination was not attained until rigid methods of 

 isolation and disinfection were carried out. Just what these 

 methods are to be in each particular case will be indicated by 

 a definite knowledge of the cause and the nature of the disease 

 in question. 



The methods for immunization that give the greatest 

 promise in aiding in the solution of the problem of the control 

 of infectious diseases are those productive of a passive immunity. 

 Although these are temporary in duration they are effective 

 immediately and consequently tend to save individuals when 

 they are applied in the period of incubation or before a possible 

 exposure. They protect the animal until the virus can be elim- 

 inated and its environment made safe. 



The advantages of introducing preventive measures are : 



1. The tendency to eliminate the virus of the disease 

 if it is present, and to keep it away if it has not already 

 appeared. 



2. The animals are free from the virus and there is no 

 danger of their subsequently developing lesions due to the 

 localization of the attenuated microorganisms. 



