vi] THE BACTERIA OF MILK 



101 



stance by decomposing it ; while some produce 

 enzymes, which in their turn cause a chemical de- 

 composition, the products of which are utilised by 

 bacteria as food materials. We have such bodies as 

 ptomaines and toxin thus produced. Old cheese is 

 on this account rather a dangerous article of food. 



Bacillus of Tuberculosis. The pathogenic microbe 

 which undoubtedly is most commonly present in milk 

 is the bacillus of tuberculosis (see Fig. 13, p. 77). As 

 we have already pointed out, the presence of this 

 bacillus is probably nearly always due to the presence 

 of tuberculosis in the cow. According to Hirschberger, 

 10 per cent of the cows living in the neighbourhood 

 of towns, where they are not treated properly, suffer 

 from tuberculosis ; and 50 per cent of these yield 

 milk containing tubercle bacilli. The virulent char- 

 acter of the bacilli in such milk has been proved by 

 experiment. In Copenhagen four out of twenty-eight 

 samples of mixed milk proved virulent when injected 

 under the skin. Freudenreich l quotes a case, cited 

 by Brouardel, where five out of fourteen young girls 

 living together in a boarding-house became consump- 

 tive, subsequent to the daily use in the establishment 

 of milk from a tuberculous cow. 



It is truly an unfortunate fact that tubercle 

 bacilli seem to be able to live in dairy products for a 

 very long time. In butter they have been found to 



1 Dairy Bacteriology, p. 43. 



