TEXT-BOOK OF BACTERIOLOGY. 341 



feeding them with tubercular sputum. The mesenteric lymphatic 

 glands are first attacked, then the intestine, spleen, liver, etc., in 

 succession. Similar changes are frequently observed vrith phthisi- 

 cal patients who swallow their sputum, thus affecting the intestinal 

 canal. A very important kind of transmission is that by the un- 

 boiled milk of cows afflicted with murrain. The investigations of 

 Bollinger, Hirschberger, and others have shown that even if the 

 udders themselves are not tubercular, the secretions of the mam- 

 mary glands may contain tubercle bacilli, and also that in nearly 

 half of all tubercular animals the milk proves to be infected. The 

 bacteria will, then, enter the human body with the food; by virtue 

 of their covering they resist the acid gastric juice (without the aid 

 of spores) and then get into the intestine, from which they are car- 

 ried to the lymphatic glands. 



The danger of drinking unboiled milk, according to these obser- 

 vations and experiences, appears very great, and it is the duty of 

 every sensible physician to strictly forbid the use of unboiled milk, 

 especially with children. 



But all the possibilities of transmission of tuberculous poison are 

 surpassed in importance by the infection by respiration. We know 

 that, as a rule, tuberculosis does not appear as an early general 

 infection of the body, but that the bacteria usually produce merely 

 local changes at the spot where they found entrance and the first 

 opportunity of showing their dangerous nature. The lungs are, 

 however, in man as well as in animals, the organ in which the mor- 

 bid processes, if not exclusively, at least principally and primarily, 

 are manifested, and this very fact points to the absorption of the 

 poison at that place. 



But, it may be asked, how do the bacilli gain access to the lungs ? 

 The tubercle bacillus is a strongly-parasitical bacterium, to which 

 the conditions necessary for development are offered nowhere out- 

 side the bodies of man and the warm-blooded animals. A trans- 

 mission of the disease can, therefore, take place only from one indi- 

 vidual to another. That it may occur from direct contact has been 

 proved; for instance, cases of tuberculosis produced in connection 

 with circumcision. 



But the same or similar conditions never pertain to the lungs. 

 We know, indeed, only one possibility of the entrance of bacteria 

 into the respiratorj' organs, viz. : the medium on which the micro- 

 organisms have developed must dry up, disintegrate into powder or 

 dust. All the former hypotheses, according to which the bacteria 

 free themselves from their surroundings and ascend, or are said to 

 be lifted upward during the evaporation of fluids, or, finally, to be 

 i6 



