TUBERCULOSIS IN CATTLE. 35 
tuberculosis from milk. Is this a common event, or is it one 
of extreme rarity? ‘That the danger is greater than the danger 
from the use of meat is clear enough from the fact that meat is 
so universally cooked and milk, at least in some countries, so 
generally consumed without cooking. But this does not tell 
us that the danger is very great. After careful study of the 
problem for many years there appears to be at the present time, 
in the minds of the scientists, an undoubted tendency to re- 
gard the danger as very much less than has been supposed. 
Indeed, so true is this that many of those who have studied the 
matter carefully are inclined to think the danger is almost noth- 
ing, and while it is not to be neglected, it is a danger which is 
so slight that it does not deserve anything like the amount of 
attention that has been given to it. The reasons for this con- 
clusion, which is, of course, a satisfactory one, both for the 
public in general and to the agricultural community, are in 
general as follows: First, as already indicated, the milk be- 
_comes contaminated only in the case of advanced tuberculosis, 
or in the case of localized udder disease. ‘The cases of ad- 
vanced tuberculosis will very rarely furnish any milk for the 
public milk supply, these animals being almost universally ex- 
cluded from the milk-producing herd. ‘The cases of udder 
tuberculosis are also rare. According to the best knowledge 
that we have, probably less than one per cent. of the animals 
suffering from the disease have tuberculosis in the milk gland. 
This, of course, reduces the chance of milk contamination very 
greatly. Furthermore, milk, as it reaches the consumer, under 
ordinary conditions, is mixed milk. That derived from one 
animal is mixed with that from many others, so that if there 
chances to be one or two animals suffering from udder tuber- 
culosis their milk is almost sure to be mixed with a large 
amount of milk from healthy animals. Thus the number of 
bacilli in a sample of milk is greatly reduced. 
Such facts, then, indicate that the contamination of the 
milk and its products is perhaps not very common. But how 
common? To this question we can give no answer. It has 
been found impractical to determine by microscopic tests 
whether milk contains the tubercle bacillus or not. There are 
methods by which it can be done, but they are at present un- 
satisfactory and wholly unreliable. The only even approxi- 
mately satisfactory method of determining whether a given 
sample of milk is infected with the germs is by inoculating it 
into the abdomen of guinea pigs. If the milk does contain the 
