185 



burger and Toyosuku 1 infected guinea-pigs subcutaneously, 

 and after the disease had become chronic, they submitted 

 these animals along with normal ones to a dust rich in 

 tubercle bacilli. The normal animals developed pulmonary 

 tuberculosis, while the tuberculous ones failed to do so. 

 Romer 2 developed chronic subcutaneous tuberculosis, and 

 then inoculated intracutaneously and intravenously, and 

 in this way demonstrated the immunity of the tissues of 

 the tuberculous animal to infection with tuberculosis. The 

 submental and cervical glands of normal guinea-pigs become 

 tuberculous on feeding with as small an amount as 0.1 

 mg. of living bacilli, but these glands are not affected when 

 tuberculous guinea-pigs are fed with living bacilli. Many 

 other investigators have experimented along the same 

 line, with like results. That the unaffected tissues and 

 organs of tuberculous men are largely immune to infection 

 with the tubercle bacillus is a matter of every-day observa- 

 tion. In pulmonary tuberculosis the sputum laden with 

 bacilli passes through the upper air passages without, as 

 a rule, infecting them. Besides, there are cases of healed 

 tuberculosis with virulent tubercle bacilli in their expec- 

 toration. There are tuberculosis carriers just as there are 

 typhoid carriers. 



Koch tried various methods in his attempts to immunize 

 animals to tuberculosis. Early in his investigations he 

 tried feeding animals with both living and dead cultures. 

 For two months he fed rats exclusively on the bodies of 

 animals dead from tuberculosis. From time to time a 

 rat was killed, and most of them were found normal. In 

 a few, small nodules were detected in the lungs. But these 

 animals after feeding for weeks upon tubercular tissue, 

 developed tuberculosis promptly when inoculated intra- 

 peritoneally. Later, Koch made the following statement: 

 "All attempts to cause absorption of living or dead bacilli, 

 by administration subcutaneously, intraperitoneally, or 

 intravenously, have failed me and also other investiga- 

 tors. When dead bacilli are injected subcutaneously they 



1 Beitrage z. klin. d. Tuberkulose, xviii 2 Ibid., xiii. 



