ioo AIDS TO BACTERIOLOGY 



of typhoid bacilli in water. Provided it be sterile, organic- 

 ally polluted water such as sterile sewage does not clear 

 itself any quicker than a pure sterile water. Hewlett 

 says that in aerated water (CO 2 ), B. typhosus does not 

 survive a fortnight. 



Very different periods of survival have been found by 

 different workers, even a year in unsterilised tap water 

 having been insufficient for it to die out. 



Shellfish. Oysters, winkles, mussels, cockles, etc., 

 from contaminated water may be a source of infection 

 (see p. 207). Klein has shown that oysters readily take 

 up B. typhosus, but clear themselves of the ingested 

 typhoid bacilli if they are kept in clean water which is 

 frequently changed. The process is slower if they 

 are kept in a ' dry ' state i.e., out of the sea- 

 water. Oysters from a polluted locality clear them- 

 selves of the ingested bacilli to a less extent and 

 at a slower rate, even if kept in clean sea-water, 

 than oysters clean at starting. Oysters from a polluted 

 locality containing a large number of the B. coli very 

 rapidly clear themselves of this microbe, whether kept in 

 or out of the water. This shows that B. coli is foreign 

 to the oyster, and is rapidly destroyed by it. When, 

 therefore, it is present in the oyster, it must have been 

 derived from the surroundings. However largely infected 

 with typhoid bacilli, the oysters remain in all parts of 

 normal aspect. Cockles and mussels similarly take up 

 the typhoid bacillus, but clear themselves much more 

 slowly, particularly in the case of cockles, than do oysters. 



The Board of Agriculture and Fisheries in their Report 

 for 1912 suggested a period of quarantine in pure water 

 for shellfish before sale. 



Dust and Air. Infection through the air for any dis- 

 tance, though possible, is unlikely. In India, where 

 excreta are buried in the ground, and dust-storms are 

 frequent, water-supplies and food are sometimes con- 

 taminated by faecal-loaded debris. Where latrines are 

 employed, as in military camps, it has been found that 

 the spot from which an epidemic started was that nearest 

 to, and directly to leeward of, the filth trenches; and the 

 direction in which it spread was always down the wind. 



Flies. After feeding on excreta, and other infected 

 material, bacilli adhere to the legs and wings of these 



