252 MILK AND ITS HYGIENIC RELATIONS 



there seems to have been a rise in the percentage of farms from 

 which infected milk was obtained. 



Delepine traced the source of tubercle bacilli in a large 

 number of samples of milk and obtained the following results : 



Per cent; 



1. Tuberculous udders the cause of infection in . .78-6 



2. Tuberculous udders probably the cause of infection 



in 16-0 



3. Nothing definite to connect infection with the 



state of the cow in 5-2 



These figures were obtained after investigating the milk from 

 276 farms. 



Tubercle bacilli have been shown to occur in milk from cows 

 in whose udder no tuberculous lesion could be detected. This 

 fact is now very generally recognised, but an interesting case is 

 quoted by Delepine as showing the difficulty of detecting early 

 tuberculous lesions of the udder by inspection and palpation 

 alone. This was a case where mixed milk from three farms 

 was found to be tuberculous. All three farms were inspected, 

 but no cow having a tuberculous udder could be detected. Mixed 

 milk of the three farms was again tested and still found to be 

 tuberculous. The veterinary surgeon again inspected the farms, 

 and after lengthy examination discovered in each a cow showing 

 slight signs of disease of the udder, but in none were the symptoms 

 at all typical of tuberculosis. Samples of milk taken from each 

 of these cows all produced tuberculosis in experimental animals. 

 Further cases on the same lines are also quoted by him. 



Mitchell (i) investigated the presence of tubercle bacilli in 

 mixed milk obtained from milk shops in Edinburgh between 

 November 1913 and May 1914. Four hundred and six samples 

 were tested, of which 82, or 20 per cent., were found to be capable 

 of producing tuberculosis when inoculated into guinea-pigs. 



Mitchell gives a table showing the occurrence of tuberculosis 

 among the Edinburgh dairy cows, compiled from the medical 

 officer's reports from 1900-13. These figures afford sufficient evidence 

 to show that tuberculosis is widespread among cows generally. 



The source of the bacilli in milk need not necessarily be the 

 cow. Evidently they can also be derived from milkers suffering 

 from tuberculosis, who, as a result of dirty or careless milking, 

 contaminate the milk with the tubercle bacilli in their own saliva. It 

 seems, however, that in the majority of instances the tubercle bacilli 

 found in milk are derived from the cow herself, a conclusion which is 

 confirmed by the figures obtained by Delepine, and quoted above. 1 



1 Tubercle bacilli cannot be entirely excluded even from milk of the 

 high quality of ' certified ' milk. Helmholtz states that where the precautions 

 required for the production of this grade of milk have been fulfilled, virulent 

 tubercle bacilli have been found in the milk. Cp* also the work of Heine- 

 mann quoted above in relation to pathogenic streptococci in ' certified ' milk. 



