TUBERCULOSIS 1 79 



tubercle bacilli. He examined six flies caught in the room of 

 a tuberculous patient and found acid-fast bacilli in four of them. 

 Similar bacilli were also found in fly-faeces scraped from the 

 walls, door and furniture of the room. 



Summary. 



In making observations on ' wild ' flies it must be remembered 

 that acid-fast bacilli closely simulating B. tuberculosis are fre- 

 quently present in milk and other substances, and consequently 

 may be found in flies. The nature of these bacilli can only be 

 proved by animal inoculations. 



The experiments quoted, however, conclusively indicate that 

 flies may carry B. tuberculosis, and distribute it for several days 

 after feeding on infected material. No doubt under suitable 

 conditions they frequently infect articles of food, and in the 

 rooms of phthisical patients may infect the food daily. In the 

 production of tuberculosis the influence of dose, especially 

 the initial dose, is probably a most important factor (Cobbett, 

 1907, p. 1028), and in most cases the number of bacilli deposited 

 cannot be very great. Only the actual number of bacilli 

 deposited are ingested with the food, since even under the most 

 suitable conditions these bacilli multiply very slowly. In this 

 connection, however, the fact that flies feeding on sputum suffer 

 from diarrhoea may be of some importance. 



The experimental evidence clearly proves the desirability of 

 protecting sputum from flies, which according to all observers 

 are greatly attracted to it, but in considering their relation to 

 infection in the human subject the influence of dose must be 

 taken into consideration. 



