PATHOGENIC BACTERIA OUTSIDE THE BODY 219 



than those just mentioned. Doubtless in \\';irm seasons of 

 the year and in the tropics other organisms pathogenic to 

 animals may Yive and multiply in water or in damp soil 

 where conditions are favorable, -just as the cholera organism 

 in India, and occasionally the typhoid bacillus in temperate 

 climates do. 



(c) Most pathogenic organisms, however, when they are 

 thrown off from the bodies of animals, remain quiescent, do 

 not multiply, in fact always tend to die out from lack of all 

 that is implied in a "favorable environment," food, moisture, 

 temperature, light, etc. Disinfection is sometimes effective 

 in this class of diseases in preventing new cases. 



II. (a) The most common infectious diseases of animals 

 are transmitted more or less directly from other animals of 

 the same species. Human beings get nearly all their dis- 

 eases from other human beings who are sick; horses, from 

 other horses; cattle, from other cattle; swine, from swine, 

 etc. Occasionally transmission from one species to another 

 occurs. Tuberculosis of swine most frequently results from 

 feeding them milk of tuberculous cattle or from their eating 

 the droppings of such cattle. Human beings contract 

 anthrax from wool, hair and hides of animals dead of the 

 disease, or from postmortems on such animals; glanders 

 from horses; tuberculosis (in children) from tuberculous 

 milk; bubonic plague from rats, etc. The mode of limiting 

 this class of diseases is evidently to isolate the sick, dis- 

 infect their discharges and their immediate surroundings, 

 sterilize such products as must be handled or used, kill 

 dangerous animals, and disinfect, bury properly, or destroy 

 their carcasses. 



(6) This class of "carriers" offers one of the most difficult 

 problems in preventing infectious diseases. A perfectly 

 healthy individual may give off dangerous organisms and 

 infect others for years. Typhoid carriers have been known 

 to do so for iifty-five years. Cholera, diphtheria, menin- 

 gitis and other carriers are well known in himian practice. 

 The difficulty in detecting such individuals is obvious. 

 Carriers among animals have not been so frequently demon- 

 strated, but there is every reason for thinking that hog- 



