CHAPTER V. 

 TUBERCULIN DIAGNOSIS. 



As a member of the class of bacterial extracts, tuberculin merits especial 

 consideration, because it is used not only for 1 immunization, but also for 

 diagnostic purposes. Tuberculin diagnosis can be employed in three ways. 



1. As Koch's subcutaneous method. 



2. As the cutaneous reaction (v. Pirquet) and ointment reaction (Moro). 



3. As ophthalmo reaction (Calmette) . 



Koch's Subcutaneous Method. 



In the chapter on aggressins it was shown that when a normal animal 

 was inoculated with a certain definite quantity of bacterial extract, it could 

 readily withstand any effects of such inoculation. If, however, a similar 

 quantity was injected into an animal previously infected with the same 

 bacterium, dangerous symptoms would be in evidence and if the dose were 

 large enough, death would be likely to follow. 



With these facts for reference, the following experiments will be easily 

 understood. A number of tuberculous guinea-pigs, and a number of normal 

 ones as control, are injected with varying doses of tuberculin. After twenty- 

 four hours some of the tuberculous animals are dead, others very ill, while 

 the normal guinea-pigs remain perfectly active. Just as in the aggressin 

 experiment, we have here a bacterial product in itself possessing only slight 

 toxic qualities which has so increased the virulence of the infection already 

 existing, that an ailment which is usually of a slowly progressive nature 

 becomes transformed into an acute one, terminating in the death of the 

 animal. 



The close analogy between the experiments with aggressin as the injected 

 substance, and that of the tuberculin, will become more clear when the nature 

 of the latter is perfectly understood. 



Four to six weeks old pure cultures of the tubercle bacilli 



Derivation of grown in 5 per cent, of glycerin bouillon are filtered, and the 



Tuberculin, filtrate then evaporated down to i/io of its original volume. 



The resultant fluid, known as tuberculin, is dark brown and 



syrupy in nature, and has the quality of keeping indefinitely. 



It consists, therefore, as we see of a 50 per cent, glycerin extract of the soluble products 

 of metabolism of the tubercle bacillus. 



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