530 Tuberculosis. 



recognize the mode of infection by the seat of the oldest lesion. 

 In by no means rare instances the first lesions develop in 

 regions or organs remotely situated from the point of infec- 

 tion, apparently with preference after an infection that is not 

 intensive. In these cases the infection was transported by the 

 blood or lymph circulation without producing changes along 

 their path. This path cannot often be determined with any 

 degree of exactness and consequently it is only in rare instances 

 that an autopsy reveals evidence uiDon which reliable conclusions 

 could be based. 



The milder the infection and the greater the resistance 

 offered by the body the slower will be the development of the 

 ensuing disease. Thus it is possible to produce artificially a 

 pulmonary phthisis characterized by excessive tissue destruc- 

 tion and the formation of cavities by the introduction of com- 

 paratively small quantities of bacilli of slight virulence 

 (Baumgarten) or by inoculating animals which had been pre- 

 viously partially immunized. Under these conditions it may 

 require months for the disease to develop in guinea pigs and 

 two or three years in goats (Behring & Roemer, Nocard, De 

 Jong). According to Calmette and G-uerin a single intestinal 

 infection of calves is said to produce a tuberculous process 

 which usually heals in the course of three or four months and 

 results in a certain degree of immunity. On the other hand 

 a number of successive infections repeated at short intervals 

 may result in a progressive tuberculous process. 



According to Behring the mother's milk constitutes the principal 

 source of pulmonary tuberculosis in man. According to this author 

 infection takes place from the gastro-intestinal tract, conditions for 

 infection being particularly favorable at this period of life since, accord- 

 ing to Disses, the epithelial layer of the intestinal mucous membrane is 

 not covered with a continuous layer of mucus during the first days of 

 the infant's life. As a result, as shown by Roemer 's findings, large 

 undigested proteid molecules and also bacteria can pass unchanged 

 through the intestinal mucous membrane of new born colts, calves and 

 the small laboratory animals, while infection in adult animals is much 

 more difficult and only possitsle either after repeated ingestion of virus 

 or after a single ingestion of exceptionally virulent material in large 

 amount. The bacilli thus taken up produce a scrofulous diathesis which 

 constitutes a groundwork for the infantile infection to develop into mani- 

 fest disease in the course of years or decades. This result is favored by 

 additional infections which take place in later life, as well as by the 

 exhausting effects of deficient nutrition, catching cold, overexertion, 

 long continued confinement in poorly ventilated houses, etc. This theory 

 has also been applied to animals. However, just as its correctness in 

 regard to man is generally questioned, its applicability to cattle is doubt- 

 ful, the more so as tuberculin reactions in calves are seldom positive 

 and as the percentage of reactions increases only later, but then steadily. 



The development of the tubercle. • At the point of their 

 lodgment and propagation the tubercle bacilli give rise to an 

 inflammatory process resulting in tubercle formation. This 



