WHAT WE BREATHE 59 



respiration, for it has been repeatedly found by 

 various investigators that the air expired by 

 infected animals is free from the dreaded tubercle 

 bacteria. As in man, so in animals it is by the 

 act of coughing that tuberculous secretions are 

 discharged through the mouth and nasal passages, 

 some of which in the form of spray may enable 

 the bacilli to remain suspended in the air for 

 periods of five hours or more, whilst other portions 

 of such secretions fall on the ground or in the 

 feeding troughs, and later on, as dust, may again 

 relentlessly claim their toll of victims. 



In other cases of tuberculosis the excrementitious 

 matter becomes, of course, a fertile source of infec- 

 tion to the surroundings. The dire results which 

 may follow the introduction of a single tuberculous 

 animal into a healthy stall of cows may be realised 

 from the fact that in one instance a whole herd of 

 twenty-eight animals became in the course of one 

 year infected in consequence of the admission of 

 one diseased cow, the cow-house having previously 

 had a perfectly clean bill of health in this respect. 



On the Continent the risk of wholesale infection 

 by such means is greater than in this country ; for 

 abroad the animals are to a much greater extent 

 stall-fed, and kept shut up both winter and sum- 

 mer. A case is mentioned by the well-known 

 veterinary authority, M. Nocard, of a whole stall 



