IV BEHAVIOUR OF BACTERIA IN MILK 59 



The growth and viability of B. typhosus in milk has been 

 studied by many vyorkers. In sterilised milk it has been 

 found to survive for as long as four months (Hesse, also BoUey 

 and Field). In market milk, kept at 7°-10° C. and inoculated 

 with a massive dose of typhoid bacilli, Pfuhl found them alive 

 when examined 1 1 and 1 3 days later. Cautley added typhoid 

 bacilli to milk and recovered them after 7 days ; while Bolley 

 and Field recovered them from inoculated milk after a month. 



While typhoid bacilli grow well in fresh milk, their 

 growth is usually checked by the increased acid production. 

 According to Bassenge,^ the bacilli are killed out if the acid 

 production reaches 0'3— 0'4 per cent and acts for over 24 hours. 

 Bolley and Field,^ Heim and other workers have, however, 

 obtained different results, and certainly any degree of naturally- 

 acquired acid production in milk cannot be relied upon to 

 kill any contained typhoid bacilli. 



The typhoid bacillus has also been shown by numerous 

 investigators to live many days in butter ; for example, for 

 3 weeks by Heim, 5-10 days by Bolley and Field, 24 days 

 by Pfuhl. 



Bruck ^ showed that typhoid bacilli could be isolated from 

 cream up to 10 days, after its separation in a separator from 

 milk artificially infected with typhoid baciUi. It could be 

 isolated from the buttermilk for 10 days, and from butter 

 made from the cream for 27 days. 



Eeitz made butter, incorporated typhoid bacilli, recovered 

 them in one experiment after 10 days but not after 15 days 

 in another experiment. 



Pfuhl mixed typhoid bacilli with cheese and isolated the 

 bacilli after 24 but not after 26 days. Other workers found 

 the bacilli died out much sooner. Probably much depends 

 on the type of cheese used for the experiments. 



1 Deutsche med. TFochenscJir., 1903, xxix. p. 675. 



2 Centralbl.f. Bali., 1898, vol. xxiii. p. 881. 



3 Deutsche med. Wochenschr., 1903, xxix. p. 460. 



