IMMUNIZATION AND CURE. 201 



Immunization and Cure. 



As soon as it was learned that filtered cultures of the 

 tubercle bacillus contained a substance which was capable 

 of producing the disease in animals, various attempts were 

 made to utilize this substance for the production of immunity to 

 the disease. Up to the present time, however, all attempts 

 at immunization have been fruitless, and the question of 

 immunization against tuberculosis is still in statu quo. The 

 blood-serum of animals not susceptible to tuberculosis, and 

 attenuated and sterilized cultures of the tubercle bacillus, 

 have been used with the hope of producing a condition of 

 immunity, but without success. 



Koch's researches in this direction have been most valuable, 

 and may in the course of time be productive of the desired 

 result. He found that the remarkable pathogenic power of 

 the tubercle bacillus was due to a toxin produced by the germ. 

 Animals were injected at intervals with mixtures contain- 

 ing live tubercle bacilli, with the result that the condition 

 produced after the first injection disappeared. The same 

 was true when dead bacilli were injected. If only the first 

 injection had been given, the animal would certainly have 

 succumbed, but, as it was, some of them remained alive for 

 as long a period as nineteen weeks. 



A 50 per cent, glycerin extract of tubercle bacilli cultures 

 produced the same result. Koch named this substance tuber- 

 culin. It is a proteid substance which is insoluble in absolute 

 alcohol, and resists a temperature of 120 C. for hours. 

 Chemically it resembles the albumins. 



Healthy animals do not react to subcutaneous injections of 

 tuberculin, even as much as 2 c.c. ; but tubercular animals 

 succumb very rapidly to as small a dose as 0.6 c.c. The 

 injection of tubercular animals with very small doses of 

 tuberculin was followed by improvement in the general con- 

 dition, although complete recovery rarely occurred. Injection 

 into diseased animals is followed by a febrile reaction which 

 is sufficiently characteristic to be of diagnostic value. 



Tuberculin is prepared in the following manner: A very 

 wide 1000 c.c. flask is half filled with veal-bouillon contain- 



