82 PRINCIPLES AND PRACTICE OF MILK HYGIENE 
diluted one billion times (Ostertag).’* In the initial 
stages, when the tuberculous areas in the udder are small 
and isolated, the tubercle bacilli are less numerous, num- 
bering about 1000 per c.c. While such milk must be 
diluted about 1000 times to render it non-virulent when 
injected into guinea pigs, it may be repeatedly fed to 
them undiluted without producing tuberculosis. 
As to the frequency of tuberculosis of the udder, in 
the post-mortem examination of 1200 cattle reacting to 
the tuberculin test, nearly all of which were dairy cows, 
Pearson found the udder tuberculous in 104, or 5.75 per 
cent. Ostertag estimates that the disease is present in 
the udder of 0.1 to 0.8 per cent. of all cows. In consider- 
ing the frequency of tuberculosis of the udder, the large 
number of bacilli present in the milk in advanced cases 
must be remembered. The milk of one cow affected with 
advanced or extensive tuberculosis of the udder can infect 
thousands of quarts of milk from other cows, if mixed 
with it, and may even render the entire supply of a 
small town infectious. 
(b) Cows with Apparently Normal Udders but 
Showing Clinical Symptoms in Other Organs or Parts.— 
Milk from cows in this condition frequently contains 
tubercle bacilli. It appears very probable that the udder 
is actually diseased when tubercle bacilli are eliminated 
in the milk of such cows. The udder may be tuberculous 
and yet be apparently normal. The disease is always 
extensive when clinical symptoms are present, and 
usually it is generalized—tubercle bacilli have repeatedly 
invaded the blood stream and have had abundant oppor- 
12 Zeitschr fiir Fleisch u. Milchhy., pp. 26 and 27, No. 2, 
vol. xxiii. 
