76 PRINCIPLES AND PRACTICE OF MILK HYGIENE 
Koch’s announcement was made, some thirty-five or forty 
investigators in different parts of the world have at- 
tempted to transmit human tuberculosis to cattle and 
all have succeeded but one. 
As to the other point upon which Koch based his views, 
the frequency of primary tuberculosis of the digestive 
tract or attached lymph glands, we learn from the in- 
vestigations of others that, while this form of tuberculosis 
is rare in adults, the proportion of cases found in children 
by different investigators is extremely variable, ranging 
from 12 to 87.8 per cent.; consequently the statistics col- 
lected by any one or two men cannot be accepted as 
representing the percentage of cases in which the lesions 
are primary in the digestive tract or attached lymph 
glands. Evidence has also been produced by the experi- 
ments of Mohler, Ravenel, Calmette, and others that 
tubercle bacilli may be introduced through the digestive 
tract and primary lesions established in the lungs or 
thoracic lymph glands without producing any lesions in 
the intestines or mesenteric lymph glands. 
Koch’s views were not accepted by many of those who 
had made a special study of tuberculosis, and his an- 
nouncement instigated a vast amount of research work. 
Commissions were appointed by the British and German 
governments to investigate the relation of bovine to 
human tuberculosis, and other official bodies, and many 
individuals also took up the study of the subject. Koch 
contended that it could be assumed that the infecting 
material had been ingested with the food only when 
primary lesions were found in the digestive tract or its 
attached lymph glands, and that only those cases in which 
tubercle bacilli of the bovine type were demonstrated in 
the lesions could be regarded as having been infected by 
