BACTERIA : NUMBER AND KIND 305 



would be less harmful than a similar number of B. colt 

 or other organisms derived from dung, putrescent 

 substances or sewage-polluted water. 



The bacteria of the greatest importance from a 

 hygienic point of view are the pathogenic species and 

 those which indicate contamination with dirty water, 

 sewage, faeces and similar objectionable materials. The 

 examination of milk for the germs of disease is beyond the 

 scope of this work. The exact and certain determination 

 of the pathogenic character of many of them involves 

 inoculation experiments upon animals, and no other 

 method will give really reliable evidence of the presence 

 or absence of B. tuberculosis. 



(i) Acid-fast Bacteria. It is however advisable to 

 test milk for acid-fast organisms in the manner indicated 

 in Ex. 150, and if found the further examination in 

 other ways may be undertaken by the proper authorities 

 if necessary. 



(ii) B. enteritidis sporogenes. As mentioned later 

 (p. 330), Klein and others believe that Bacillus enteri- 

 tidis sporogenes is responsible for epidemics of diarrhoea 

 among children, but the matter is still in dispute. 



Apart from this aspect, tests for Bs. enteritidis are 

 useful, since it is a very common inhabitant of animal 

 faeces and its presence may be taken as an indication 

 of pollution for this source. According to Orr's investi- 

 gation, it would seem that the farmer and not the 

 dairyman is chiefly responsible for its occurrence in milk. 

 As it does not multiply in milk except under anaerobic 

 conditions its occurrence in I c.c. or less of any sample 

 may be taken to denote unclean conditions at the farm. 



Ex. 145. Examine samples of milk for the presence of Bacil- 

 lus enteritidis sporogenes by the method described in Ex. 151. 



u 



