TRANSMISSION OF DISEASES BY INSECTS 243 



The house fly is well adapted by its structure and habits to carry 

 bacteria. The adults often feed on substances contaminated with 

 typhoid or other bacteria and these infected substances cling readily 

 to the hairs of the insect, especially those of the feet, and to the pro- 

 boscis. The larvae develop chiefly in horse manure, but also in other 

 kinds of excreta, some of which may contain virulent typhoid bacilli. 



Transmission by Flies. During the Spanish- American war ty- 

 phoid fever occurred in every American regiment and raged in many of 

 the concentration camps, in consequence of which a special commission 

 was appointed to investigate the origin and spread of the disease in the 

 army. A report by one of the members of the commission, Doctor 

 Vaughan, presents the following conclusions: 



"a. Flies swarmed over infected fecal matter in the pits and then 

 visited and fed upon the food prepared for the soldiers at the mess tents. 

 In some instances where lime had recently been sprinkled over the con- 

 tents of the pits, flies with their feet whitened with lime were seen walk- 

 ing over the food. 



"b. Officers whose mess tents were protected by means of screens 

 suffered proportionally less from typhoid than did those whose tents 

 were not so protected. 



"c. Typhoid fever gradually disappeared in the fall of 1898, with 

 the approach of cold weather, and the consequent disabling of the fly. 



"It is possible for the fly to carry the typhoid bacillus in two ways. 

 In the first place, fecal matter containing the typhoid germ may adhere 

 to the fly and be mechanically transported. In the second place, it is 

 possible that the typhoid bacillus may be carried in the digestive organs 

 of the fly and may be deposited with its excrement." 



Similar conclusions in regard to the agency of flies in the spread of 

 enteric fever among troops have been reached also by investigators in 

 Bermuda, South Africa and India. 



Firth and Horrocks fed house flies on material contaminated with 

 Bacillus typhosus and then obtained cultures of the bacillus from objects 

 to which the flies had access. In another experiment they got cultures 

 from the heads, bodies, wings and legs of such flies. Other investigators 

 have obtained Bacillus typhosus from flies captured in rooms occupied 

 by typhoid cases. 



Faichnie caught flies in a place where there was an outbreak of ty- 

 phoid fever, held them on a sterilized needle and passed them through a 

 flame until legs and wings were scorched; after which he obtained the 



