MILK-BORNE INFECTIONS 459 



stroyed and the surviving ones attenuated. The danger from 

 inhalation is naturally greater in houses than in the open air, 

 because the effect of sunshine indoors is limited and the dust 

 raised may carry tubercle bacilli that have not been seriously 

 affected by Ught. 



Communication of tuberculosis through sputum is probably 

 not as important as has been generally believed. The baciUi 

 which gain entrance through the intestinal tract are carried there 

 with food. Bovine bacilU introduced with milk or milk products 

 have not been exposed to adverse conditions as have bacilli in 

 sputum. In milk and butter they have been shown to retain 

 virulence for several months, and they can, therefore, reach the 

 intestinal tract in fully virulent condition. The relation of 

 bovine tuberculosis to human health hinges on the question of 

 infectiousness of tubercle bacilh of the bovine type for man. 



Koch stated in 1901 that the question whether man is sus- 

 ceptible to bovine tuberculosis has not been definitely settled, 

 but that if such a susceptibility exists it is very rare. He stated 

 that he beheved that no special protective measures were neces- 

 sary. Von Behring takes the opposite view, believing that tuber- 

 culosis in man is commonly contracted in childhood through 

 drinking infected milk. Both views may be extreme, but an enor- 

 mous amount of work has shown that man is susceptible to bovine 

 tuberculosis, and that, especially among children, the percentage 

 of cases due to bovine infection is considerable. It is unneces- 

 sary to discuss in detail the work of many European and American 

 investigators whose results are very concordant. Commissions 

 were appointed by the English and German governments to 

 investigate the question and a great deal of work has been done 

 in the government laboratories in Washington, D. C, and in a 

 number of State Experiment Stations. The most comprehensive 

 work on this subject was pubKshed in two papers by Park and 

 Krumwiede. These authors investigated 1242 cases sent to them 

 at random from various hospitals. The results show that among 

 adults of sixteen years or over suffering from tuberculosis — 1.27 

 per cent.; among children between five and sixteen years — 23.53 

 per cent.; and among children below five years — 23.21 per cent, 

 were infected with bovine tubercle bacilli. The two types were dis- 

 tinguished by cultural characteristics — ^morphology and virulence 

 for rabbits. The medium used for cultivation was glycerinated 

 ■egg medium and glycerinated potato. The presence of glycerin 

 favors clear distinction of properties. The chief differences be- 

 tween human and bovine tubercle bacilU may be summarized as 

 follows (Park and Krumwiede.) : 



