AIE 49 



taken into the bodies of the healthy animals, for the more 

 stagnant and impure the air of the stable the less will be 

 the chance that the bacteria will be carried out of the 

 building. 



Secondly, the continued inhalation of an impure atmo- 

 sphere will favour the progress of the disease in such 

 animals as become affected, by inducing a state in which 

 the natural defences of the animal body are greatly 

 weakened. The researches of recent years have shown 

 that by no means every horse that becomes infected with 

 the bacillus of glanders thereafter develops extensive lesions 

 or has its health seriously disturbed. Even in healthy 

 subjects the bacilli may find admission to the body, and to 

 a certain extent establish themselves there, but in vigorous 

 states of the animal the natural defences suffice to hold the 

 invading organisms in check, or even overcome these 

 altogether. The agencies that tend to weaken the natural 

 powers of defence against bacteria are impure air, underr 

 feeding, and excessive work, and in all probability the most 

 potent of these is the first. 



In the second class of bacterial diseases, viz., those 

 caused by germs that are capable of multiplying outside of 

 the animal body, the effect of an impure atmosphere is 

 probably even more malign. The bodies of both men and 

 the lower animals must be constantly threatened with 

 invasion by some of the bacteria which are almost ubiqui- 

 tous, and which are on the border-line of being pathogenic 

 even to those in robust health. Such organisms find their 

 favourable opportunity when they encounter an individual 

 whose natural defences have been weakened by insanitary 

 conditions, prominent among which is the inhalation of a 

 vitiated atmosphere. 



One of the important, if not the most important, factors 

 contributing to everyday immunity is pure air. 



The term ' everyday ' immunity is used to avoid clashing 

 with the pathologist by employing the term natural im- 

 munity ; and further, everyday immunity is temporary, it 

 can hardly be otherwise, and depends on the individual 



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