186 PROTEIN POISONS 



uniformly cause suppuration, and they can be easily stained 

 and detected in large numbers in the abscesses thus formed 

 after months. When injected into the peritoneal cavity 

 they are better absorbed, and I have obtained some immunity 

 in this way, but they generally cause local inflammations, 

 which lead to adhesions with stenosis and occlusion of the 

 intestine, so that a large percentage of the animals is lost. 

 When injected intravenously into rabbits, dead bacilli 

 cause tubercular nodules, similar to those observed after 

 infection, in the lungs, and in these nodules the unaltered 

 bacilli can be found after a long time. By this method 

 absorption does not proceed in the desired way. Having 

 been convinced that the unaltered bacilli could not be 

 used, I attempted to render them absorbable through the 

 action of chemical agents on them. The only method of 

 this kind which I have found effective consists in boiling 

 the bacilli with dilute mineral acid or with 'strong alkali. 

 In this way tubercle bacilli may be so changed that they are 

 absorbed in toto, and in large amount, though slowly, when 

 administered subcutaneously. But marked immunity has 

 not been reached in this way, and it seems that these chemi- 

 cal agents cause such thorough alteration in the bacillary 

 substance that its immunizing property is destroyed." 



This conclusion reached by Koch has been justified by 

 all subsequent investigators. Levy 1 has tried to prepare a 

 vaccine by such chemically indifferent substances as glycerin, 

 25 per cent, solution of milk sugar, and 10 to 25 per cent, 

 solutions of urea. The object in these experiments was to 

 kill the bacilli by the withdrawal of water and without 

 changing their immunizing properties. Levy stated that 

 these vaccines contain no living bacilli, and with them he 

 apparently increased the resistance of guinea-pigs to infec- 

 tion with tubercle bacilli, but Romer doubts the complete 

 killing of the bacilli by these agents. Heating the bacilli 

 to 70 or 80 has failed to furnish an effective vaccine. 

 Lowenstein 2 tried to prepare a vaccine by exposing tubercle 



1 Med. Klinik, 1905, 1906; Centralbl. f. Bak., xlii, xlvi, and xlvii. 



2 Zeitsch. f. Tuberkulose, 1905, vii. 



