INFLUENCE OF DISEASE UPON MILK 87 
culous cows is diluted more or less with the milk of non- 
infected cows. The extent of the dilution will depend 
upon the method of handling the milk. Ordinary mar- 
ket milk, however, is frequently the mixed milk of sev- 
eral herds, but at any rate it is the mixed milk of a number 
of cows in the same herd. It has been demonstrated that 
the milk of cows affected with advanced or extensive 
tuberculosis of the udder may render the entire supply 
infectious when mixed with milk from other cows which 
are not tuberculous; but this is not true of milk from cows 
which do not show clinical symptoms of the disease. 
Miiller and Hessler examined by inoculation samples 
of mixed milk from 2949 herds, each sample representing 
the milk from 30 to 200 cows. Tubercle bacilli were 
present in the samples from 156 herds. All of these 
herds except five were found to contain cows affected 
with udder tuberculosis or other forms of open tuber- 
culosis. In the five herds in which tuberculosis was not 
established clinically, Hessler is of the opinion that the 
tubercle bacilli were eliminated in the feces by cows with 
incipient cases of open lung tuberculosis which had not 
yet become perceptible. The other 2793 herds, in the 
milk samples from which tubercle bacilli were not demon- 
strated, certainly contained a considerable number of 
cows which would have reacted to the tuberculin test, 
judging from the extent to which tuberculosis was known 
to exist in the district in which they were located. 
Delépine examined the milk from 1885 farms and 
found tubercle bacilli in the samples from 294 farms. 
The cattle on 276 of these farms were examined and on 
190 farms one or more cows were found affected with | 
tuberculosis of the udder, a bacteriological examination 
of the individual milk being necessary in some cases to 
