158 THE MORE CHRONIC INFECTIOUS DISEASES 



beings. That is, no serum can be procured which will 

 give a passive immunity. 



Tuberculin. The poisons made in cultures and used 

 for the tuberculin test in the form of Koch's tuber- 

 culin have already been mentioned. There are many 

 forms of tuberculin which are incidentally modelled 

 after Koch's plans. His original was a broth upon 

 which the bacteria had grown, but freed of living forms 

 and reduced by evaporation to one-tenth its original 

 volume. This contained both the endo- and extra- 

 cellular toxins. His later forms consisted of killed 

 bacteria, of a watery extract from them and lastly, 

 living bacteria so reduced in virulence that they could 

 not produce tuberculosis. These are all tuberculins, 

 the last forms being called vaccines also. Not only 

 are these toxic solutions of value for diagnosticating 

 tuberculosis, but they may also be used in treatment, 

 the purpose being to induce some active immunity 

 to the tubercle bacillus poisons. They are injected 

 under the skin of tuberculous patients, beginning with 

 extremely minute doses, too small to produce the 

 tuberculin reaction described above. We increase 

 the quantity gradually until the patient can endure 

 large amounts. It is maintained that this treatment 

 is very beneficial and that a slight immunity is achieved. 

 Opinions vary as to its value, but those who have had 

 longest experience usually testify to its efficacy, 

 although no one maintains that it is a cure-all, but 

 merely another means of treating this serious disease. 

 This is in reality an active immunization during the 

 course of the disease, but it has not been found possible 

 to inject a healthy person in the same manner and 

 thereby increase his resistance to tuberculosis. 



