306 EXPLANATIONS OF THE TUBERCULIN REACTION 



we should expect them to be if tuberculin were diffusing from 

 their lesions. 



Ehrlich's views are quite similar to Koch's, and he regards the 

 reaction as due to the effect of the tuberculin on tissues which are 

 injured by it at the time of the injection, and in which a slight 

 extra dose is sufficient to turn the scale. 



Others have thought that the reaction is indicative of a hyper- 

 sensitiveness of the patient to tuberculin, using the term in the 

 sense in which we employed it in dealing with the toxins. This, 

 of course, is true, but it scarcely seems a sufficient explanation in 

 itself. We shall revert to the subject after giving an account of 

 some most remarkable discoveries that have recently been made 

 concerning this subject. 



Marmorek holds in all probability correctly that tuberculin 

 is not to be regarded as in any sense the true toxin of the tubercle 

 bacillus. This is only formed when the organism is living para- 

 sitically in the tissues, or in artificial conditions bearing a very 

 close approximation thereto, not in such a simple medium as plain 

 broth. Tuberculin has this effect on a tuberculous animal : it 

 stimulates the tubercle bacilli to a sudden and energetic production 

 of toxin, which gives rise to the local reaction, and, passing into 

 the vessels, to fever and its concomitant general phenomena. 

 There is nothing inherently improbable in this suggestion, except 

 that no reason is forthcoming as to the way in which tuberculin 

 exerts this very remarkable action, but there is little direct evidence 

 in its favour. The toxin which Marmorek claims to have pro- 

 duced by the application of this principle is so weak as not to 

 be worth calling a toxin. 



Wassermann and Briick point out that the extremely minute 

 amount which must be present in the blood at a given time leads 

 to the supposition that the tuberculin injected must leave the blood- 

 stream and become concentrated in the region of the tuberculous 

 focus. Thus, if a person with 5,000 c.c. of blood reacts to an injec- 

 tion of i milligramme of tuberculin, the dilution will be i : 5,000,000, 

 and they find that this dilution injected directly into a tuberculous 

 lesion gives absolutely no reaction. They then proceed to argue 

 that this attraction of the tuberculin from the blood must be due 

 to the presence in the tuberculous tissue of an antitoxin or anti- 

 tuberculin. They investigated the presence or absence of this 

 substance by means of the method of fixation of the complements. 

 Extracts of tuberculous tissues, when mixed with tuberculin, 



