NINTH ANNUAL YEAR BOOK— PART X 481 
Concerning the infectious nature of milk secreted by tuberculous cows, 
authorities have universally agreed that when the udder itself is in the 
slightest degree involved, the milk possess infectious properties, and is 
therefor dangerous. Tubercle bacilli have been found in large numbers 
in the milk and the udder under such circumstances. Unlike other af- 
fections of the udder, tuberculosis of this organ does not at once 
change the appearance and the quality of the milk secreted. Bang 
states that for at least a month after the disease has appeared the milk 
is normal in appearance and may be consumed and sold without arousing 
the suspicion of the owner. There is, therefore, considerable danger 
involved in this disease, and the necessity for the careful inspection of 
dairy cows seems more urgent than ever before. 
Authorities are, however, not fully agreed as to whether the milk from 
tuberculous cows in which the udder is apparently not invaded by tha 
disease should be considered dangerous or not. Some are inclined to 
believe that the milk secreted by healthy udders is never infectious, even 
when the lungs or other organs are affected; that, in other words, the 
tubercle bacilli are rarely, if ever, separated from the lesions which they 
produce, and that the udder itself must be diseased before tubercle bacilli 
can appear in the milk. Experiments made with the milk of tuberculous 
cows in which there were no indications of udder disease do not bear out 
this theory, since authorities still believe that the udder s diseased when 
the milk is infected, but that the disease escapes observation. However 
this may be, the fact that the udder may be diseased and the disease not 
recognizable, simply casts suspicion upon all milk from tuberculous ani- 
mals. We know that the milk of tuberculous cattle may or may not con- 
tain tubercle bacilli when the udder is apparently free from disease. But 
we have no rapid method of determining whether, in any given case, the 
milk contains tubercle bacilli or not. Moreover, the bacilli may be absent 
at one time and present at another in milk from the same cow. When we 
consider therefore, the extent of tuberculosis and the hidden character of 
the disease, a certain amount of suspicion rests upon all milk. Fortu- 
nately tubercle bacilli are readily destroyed by the temperature of boiling 
water, and hence both meat and milk are made entirely safe, the former 
by the various processes of cooking, the latter by boiling for a few 
moments. Until better means of diagnosis are at hand it is incumbent 
upon all communities to have dairy cows examined or inspected, at least 
to the extent of finding out whether the udder shows any signs of dis- 
ease. If this is detected the affected animal should be killed at once, or 
else all opportunity for the sale of such milk removed by appropriate 
measures. The dangers from infected milk might by these means be very 
materially lessened. 
Recently there has been much discussion of the question as v/hether 
human and animal tuberculosis are identical diseases and as to the pos- 
sibility of the tuberculosis of animals being transmitted to man or that 
of man being transmitted to animals. 
The fact that tubercular material from human subjects often failed 
to produce serious disease in cattle was observed by a number of the 
earlier investigators who experimented with such virus. It was the ex- 
