INFLUENCE OF DISEASE UPON MILK 89 



each according to the stage of lactation and once each 

 week the milk from each group was put into a separate 

 can, the cows being groomed and milked in the usual 

 manner by the regular attendants. A sample of milk 

 was taken from each can for examination. Two guinea 

 pigs were inoculated from each sample one with the 

 cream and one with the sediment. This was repeated each 

 week for six weeks. Then the cows in the stable were 

 again examined in the same way and, no symptoms indi- 

 cating tuberculosis being found, samples of milk were 

 collected and examined as before once a week for another 

 period of six weeks. Altogether, 96 guinea pigs were 

 inoculated. Thirty died of intercurrent disease and the 

 other 66 were chloroformed two months after inoculation. 

 A post-mortem examination was made of every animal, 

 but in no instance were any lesions of tuberculosis found. 

 One of the cows in the experiment had reacted to tuber- 

 culin over 8 years before, one 7 years, two 6 years, two 4 

 years, two 3 years, two 2 years, one 1 year and one 4 

 months before. 



These observations show that non-clinical reactors 

 play a minor role in the infection of market milk with 

 tubercle bacilli, even when the virulence of the milk is 

 tested by the delicate fnoculation test. That there is a 

 vast difference between the number of tubercle bacilli 

 necessary to produce infection by the mouth and by in- 

 oculation has been demonstrated by a number of investi- 

 gators. Ostertag and others have shown that two and a 

 half million times more material is required to infect an 

 animal by feeding than by inoculation. Schroeder and 

 Cotton found that milk which would produce tubercu- 

 losis in guinea pigs when 5 c.c. was injected into the 

 peritoneal cavity could be fed 30 days without producing 



