FLIES AND TYPHOID 425 



washed by water through a thickness of 18 in. Neither 

 virgin nor sewage-polluted soils differed much in these 

 respects. 



Vitality of B. typhosus in dust, fomites, etc. Firth and 

 Horrocks found the B. typhosus to be alive in soil dry 

 enough to form dust for as long as twenty-five days, and 

 consider that infective material can be readily transmitted 

 from dried soil and sand by means of winds and air- 

 currents. Doubtless much depends on the degree of 

 dryness of the substratum. From khaki drill and serge 

 inoculated with cultures the bacillus was recoverable for 

 from ten to twelve weeks, and for from ten to seventeen 

 days from the same materials fouled with enteric faeces. 



Semple and Grieg, 1 with cloth and blanket infected with 

 typhoid urine, failed to obtain the bacillus after seventeen 

 days. This, however, was in India, and the survival of 

 the typhoid bacillus on fomites probably greatly depends 

 on the degree of drying of the material. A striking 

 instance of the conveyance of infection by fomites was 

 that of the blankets used in the South African War and 

 brought to this country, which gave rise to many cases of 

 typhoid fever. 



Firth and Horrocks demonstrated that house-flies can 

 convey infection from enteric excreta or other polluted 

 material to objects on which they settle or feed, and 

 the Commission which investigated the prevalence of 

 enteric fever in the Spanish-American War ascribed to 

 flies the principal part in the dissemination of the disease 

 (see also p. 465). 



It is commonly supposed that sewer-gas is at least a 

 predisposing cause to enteric fever, diphtheria and ton- 

 sillitis, but the nature of this relationship has given rise 

 to discussion. Some have considered that the specific 

 organisms are present in the emanations from sewers, 

 1 Sc. Mem. Gov. of India, No. 32, 1908. 



