364 A MANUAL OF BACTERIOLOGY 



by the use of broth cultures for infection, the broth added 

 causing a multiplication of the saprophytes. Firth and 

 Horrocks l similarly conclude that the typhoid bacillus 

 displays no tendency to increase in numbers, nor to grow 

 upwards or downwards in soil, though it may be washed 

 by water through a thickness of 18 inches. 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, 2 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 enteric infective material from specific excreta 

 or other polluted material to objects on which they settle 

 or feed, and the Commission which investigated the preva- 

 lence of enteric fever in the Spanish- American War ascribed 

 to flies the principal part in the dissemination of the disease 

 (see also p. 389). 



1 Brit. Med. Journ., 1902, vol. ii, p. 936. 



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



