CHAPTER V. 



TUBERCULIN DIAGNOSIS. 



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

 especial consideration, because it is used not only for immunization, but 

 also for diagnostic purposes. Tuberculin diagnosis can be employed in 

 several ways. 



1. As Koch's subcutaneous method. 



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

 (Moro and Doganoff). 



3. As intracutaneous reaction. 



4. As ophthalmo reaction (Calmette). 



Koch's Subcutaneous Method. 



In the chapter on aggressins it was shewn 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 possess- 

 ing only slight toxic qualities but 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 in- 

 jected 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 tubercle bacilli grown 



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



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



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



syrupy in nature, and keeps indefinitely. 



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