THE PRESENCE IN MILK OF CERTAIN ORGANISMS 251 



number 88, or 17 per cent, of all the herds, contained infected cows. 

 In the southern part of Wisconsin State, which had been settled for a 

 longer period than the other parts and which has a denser popula- 

 tion, 43,176 cows had been examined. Of these animals 4570, 

 or 10 -5 per cent., gave a positive reaction. The cows belonged 

 to 2164 different herds, of which 941, or 43*4 per cent, of all the 

 herds, contained infected animals. 



The difference in the rate of incidence of tuberculosis in the 

 cattle of the two portions of the state is very striking. 



Campbell, in 1909, investigated the presence of tubercle bacilli in 

 the general milk supply of Philadelphia. He took 130 samples 

 of market milk and found that 18 contained tubercle bacilli. 

 Seven of the inoculated guinea-pigs died before they could be ex- 

 amined for tuberculosis, but excluding these the precentage of positive 

 samples was 13-8. Samples of milk sold as pasteurised milk were 

 also examined, and of these 8*3 per cent, gave positive results. This 

 fact shows the unreliability of pasteurisation in procuring a safe 

 milk supply. This point is considered further in Chap. XIX. 



Delepine, dealing with the milk supply of Manchester between 

 the years 1897 and 1913, examined 7681 samples of milk, of which 

 671 were found to contain tubercle bacilli, or 8-7 per cent, of the 

 total. The figures given show that there had been a considerable 

 fall in the percentage of positive samples since the commencement 

 of the investigation, the percentage for the first two years having 

 been 17*2 per cent. 



These figures apply only to milk samples and do not give any 

 indication of the number of individual cows giving tuberculous 

 milk. Delepine points out that one cow giving tuberculous milk 

 can infect a much greater quantity of milk than her own, when the 

 milk from several cows is mixed together. In one experiment he 

 took some milk from a cow whose udder was in a state of advanced 

 tuberculous mastitis, and diluted it with various quantities of cows' 

 milk which contained no tubercle bacilli. The mixed milk of 

 various dilutions was inoculated into different guinea-pigs, and the 

 results showed that one part of the tuberculous milk was capable 

 of infecting 100,000 parts of non-tuberculous milk. Delepine 

 adds that had the dilution been pushed further it is probable that 

 the milk would have been found capable of infecting 1,000,000 

 parts of non -tuberculous milk. Evidently, therefore, the samples 

 of tuberculous milk give no indication of the absolute number of 

 infected cows. 



Delepine gives figures for the number of farms upon which 

 tuberculous cows were found, and from which milk was supplied to 

 Manchester during the years 1896 to 1913. The average number 

 of farms containing infected cows for the whole period was found 

 to be I0'4 per cent., the figures varying from 16-8 per cent, in the 

 first four years to 6-3 per cent, in one of the later years. The figures 

 showed a marked tendency to fall up to the year 1910, since when 



