CONGRESS ON TUBERCULOSIS. 
463 
taining tubercle bacilli. It is true that opinions with regard to 
this point are not absolutely unanimous, but there is ample evi¬ 
dence to justify the assertion that as a rule the milk is not dan¬ 
gerous until the udder itself becomes diseased. The experi¬ 
ments pointing to an opposite conclusion form only a small 
minority, and the results obtained in most of them were proba¬ 
bly due to carelessness on the part of the experimenter.. In a 
few of the cases in which the milk of an apparently healthy 
udder was found to be infective, it is probable that the gland 
tissue was in reality diseased, though not to an extent discover¬ 
able without microscopic examination. The important ques¬ 
tion, therefore, is not what proportion of milch cows are tuber¬ 
culous, but what proportion of them have tuberculous udders. 
Some authorities have estimated this to be as high as ten per 
cent., but the proportion is certainly much less than that in 
Great Britain. My own experience leads me to think that about 
two per cent, of the cows in the milking herds in this country 
are thus affected. Now, the milk secreted by a tuberculous 
udder always contains tubercle bacilli, and it sometimes con¬ 
tains enormous numbers of them, and when these facts are ap¬ 
prehended one begins to realize the seriousness of the danger to 
which, in the present state of affairs, those who drink uncooked 
milk are exposed. But there are one or two considerations that 
make the danger greater than the mere statement of the number of 
cows affected would at first sight indicate. In the first place, the 
udder disease is not attended by any pain or tenderness in milk¬ 
ing, and the milk for a considerable time after the udder has be¬ 
come manifestly diseased may appear quite wholesome, though 
in reality it is charged with the germs of tuberculosis. It there¬ 
fore often happens that the gravity of the condition is not 
realized by the milker or the owner of the cow, and the milk 
continues to be sold for human consumption. There is scarcely 
any room for doubt that if it were sold and consumed unmixed 
with other milk, some of the persons partaking of it would be¬ 
come infected. In practice it is usually mixed with the milk 
from other cows that have healthy udders, and thus the germs 
are distributed among a larger number of persons. Even tuber¬ 
culous milk that has been thus much diluted may prove infec¬ 
tive, but the danger to the individual consumer is in inverse 
proportion to the degree of dilution. 
Since about one cow in fifty is the subject of tuberculosis of 
the udder, and the average number of cows in the milking 
herds of this country is less than fifty, it follows that the majority 
