CHAPTER XI 

 "REACTIONS" AND SIMILAR PHENOMENA 



NOT long after the discovery of the tubercle bacillus Koch found 

 that the effects of an inoculation of living cultures of the organism 

 were quite different in normal and in tuberculous animals. If a 

 normal animal is inoculated by scarification of the skin the 

 wound soon heals, and in about a fortnight a hard nodule forms. 

 This ulcerates, and remains an open ulcer until the animal dies. 

 If a second inoculation be made after the first has run its course 

 to the stage of ulceration, the process is profoundly modified. No 

 nodule is formed at the site of the second inoculation, but the 

 tissue round the first becomes hard, dark-coloured, and finally 

 necrotic, and may be shed en masse and the lesion undergo com- 

 plete cure. Koch found, further, that this change might be 

 brought about by injections of dead cultures even after they had 

 been boiled. He found, too, that a large dose of these killed 

 cultures (which would cause nothing but local suppuration in 

 normal animals) would kill a tuberculous guinea-pig in a short 

 time six to forty-eight hours the symptoms being fever, acute 

 inflammation, running on to necrosis, in the region of the tubercu- 

 lous lesions, and in some cases generalization of the bacilli 

 throughout the body. When very minute doses were used he 

 found, on the contrary, that improvement might occur, and the 

 tuberculous ulcer become cicatrized over. 



This was made the basis of a method for the treatment of 

 tubercle in man. But Koch found the use of killed cultures 

 inconvenient, since the bacilli w r ere but slowly absorbed, and 

 might give rise to abscesses. He argued that the effect was 

 evidently due to some soluble substance which diffused out of the 

 bacilli, and after long research prepared the substance which is 

 now so familiar as the old tuberculin. It is a solution in 40 to 50 per 

 cent, glycerin of the soluble products of the tubercle bacillus, and 

 is prepared by cultivating that organism for several weeks in 



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