IV 



BEHAVIOUR OF BACTERIA IN MILK 61 



also failed to find this organism after one or two days in 

 cheese. 



Micrococcus melitensis grows rapidly in sterile milk with 

 rapid alkali production, but without producing visible change. 

 It is found in the milk of a large proportion of the goats in 

 Malta, producing no visible alteration in the milk. 



Tubercle bacilli will grow in sterilised milk, the milk 

 remaining unchanged. They grow so slowly in milk that in- 

 vestigations as to their rate of growth are of no practical 

 significance, while we have abundant evidence that they retain 

 their virulence and viability all the time milk is likely to be 

 kept unconsumed. Living tubercle bacilli have been found in 

 butter made as long as five months previously from milk con- 

 taining tubercle bacilli, but they appear to usually die out 

 earlier. They apparently die out more rapidly in salt than in 

 fresh butter. 



Teichert 1 investigated a large number of butter samples 

 obtained from thirty-six different dairies. None of the samples 

 more than 18 days old set up tuberculosis in guinea-pigs. 

 Teichert concluded that in the salt butters tubercle bacilli 

 lose their virulence in about three weeks. 



Mohler, Washburn, and Eogers 2 carried out an interesting 

 series of experiments. Three samples of butter were made, 

 the first from milk artificially inoculated with tubercle bacilli 

 from a culture, the second and third from the milk of a cow 

 suffering from udder tuberculosis, the milk containing great 

 numbers of very virulent tubercle bacilli. The first two were 

 salted in the usual proportions of 1 oz. of salt to 16 oz. 

 of butter, the third sample was left unsalted. The samples 

 of butter were kept in cold storage, while from time to time 

 guinea-pigs were fed and inoculated. The samples were tested 

 when first made, after storing 10 days, after 60 days, and 

 after 5 months. The results showed that each of these samples 

 harboured virulent tubercle bacilli throughout the entire storage 

 period, and that at any time they were capable of setting up 

 tuberculosis in guinea-pigs when inoculated intra-peritoneally. 



Tubercle bacilli may also live for some time in cheese. 



1 Klin. Jahrb., 1904, xii. p. 467. 



2 Bulletin No. 41, Public, Health and Marine Hospital Service, U.S.A., 1908, 

 p. 494. 



