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 % to 37.8 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 tKe 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 



