DISTRIBUTION OF BACTERIA 95 



walks, resemble miniature brushes (Plate I, fig. 2), from which no 

 cleansing can remove the organisms once these appendages have 

 been defiled, with the result that they contaminate whatever 

 substance they subsequently visit ivithin a certain length of timer 

 (Hewitt, 1912, p. 72.) 



These facts have been well recognized for years, and many 

 writers during the latter part of the nineteenth century either 

 attributed infection in certain cases to contamination by flies, or 

 uttered warnings on the subject. From time to time the fact 

 that a house-fly can carry micro-organisms on its legs, etc., was 

 demonstrated experimentally b)- allowing a fly to walk over the 

 surface of a culture and then causing it to walk over sterile culture 

 media, on which the bacterium employed could be cultivated 

 subsequently. By simple experiments of this nature, which 

 closely resemble the ordinar}' methods adopted in transferring 

 bacteria from one culture medium to another by means of a 

 platinum needle, it was shown that flies can transfer a number 

 of well-known disease producing bacteria, but very few attempts 

 were made to ascertain how long the flies remained infective or 

 whether they could carry the bacteria in any other way. The 

 small number of more elaborate, usually isolated experiments 

 which were made, are quoted in the chapters dealing with the 

 specific diseases. 



During 1909 and 19 10 the writer (Graham-Smith, 1909, 19 10) 

 carried out for the Local Government Board Enquiry a large 

 number of experiments on flies with B. pi'odigiosns, and several 

 disease producing bacilli, including B. anthracis (see Chapters 

 XIII — XVIII). 



For the preliminary experiments B. pj-odigiosns was selected 

 because it is an organism which is easily cultivated and identified 

 on plate cultures. Moreover it seemed likely that the results 

 would give some information as to the length of life of other 

 non-spore-bearing and less easily recognizable bacteria under 

 similar conditions, and afford some indications of the best 

 methods of procedure in making investigations on them. 



For the same reasons the spores of B. anthracis were employed 

 to demonstrate the persistence of spores. 



