200 ACTIVE IMMUNIZATION 



and upon the progress of the lesion at the site of the primary inocu- 

 lation. Since killed-off cultures, however, though quite efficacious, 

 were "apparently not resorbed from the point of inoculation, nor 

 otherwise removed, but remained there undisturbed and produced 

 abscesses," Koch attempted so to modify his vaccine as to separate 

 the curative from the harmful principle. The result was his famous 

 tuberculin. This was prepared by growing tubercle bacilli for eight 

 weeks in 4 per cent, glycerin-peptone-bouillon, and then concen- 

 trating the culture at 90 C. to one-tenth of its original volume. The 

 resultant material thus actually represents a 40 per cent, glycerin 

 extract of the original culture, which is finally passed through a 

 porcelain filter, and is then ready for use. 



This is hardly the place to narrate the history of the introduction 

 of Koch's tuberculin into clinical use, the hopeful anticipation with 

 which it was received, and the sorrowful disappointment that was 

 the outcome of the earlier clinical trials. Suffice it to recall that 

 the medical profession for a while expected the impossible, and that 

 the non-realization of these expectations caused the pendulum to 

 swing the other way, and to such a degree in fact that even now 

 the very word "tuberculin" to most minds suggests failure. This 

 was largely the outcome of the indiscriminate use of the substance, 

 and the fact that in most cases the final verdict was based upon a 

 trial, scarcely extending over a longer period than a month or two, 

 even in cases where subsequent experience has shown that recovery 

 under its use is possible. That this may indeed occur, and more 

 promptly so than under an expectant plan of treatment, seems to be 

 undeniable ; but detailed clinical studies have shown that the success- 

 ful immunization of the tubercular individual is frequently beset 

 with great difficulties, owing to the existence or development of a 

 curious and most remarkable hypersusceptibility, in consequence of 

 which every injection is followed by a reaction which is evidently 

 detrimental to the patient. 



In our account of anaphylaxis we have already drawn attention 

 to this occurrence and have studied the mechanism which underlies 

 its production. I would merely emphasize at this place that in 

 tuberculosis probably more than in any other of the infectious 

 diseases, are anaphylactic processes responsible for many of the 

 phenomena which go to make up the clinical picture of the disease. 

 In the days when Koch's early work on tuberculin was done, nothing 



