" REACTIONS AND SIMILAR PHENOMENA 301 



glycerinated veal broth in a thin layer, so that there is an abundant 

 supply of oxygen. This culture is evaporated to one-tenth of its 

 volume and filtered through a Chamberland filter. There are 

 numerous slight modifications in the process of manufacture, 

 but they are unimportant. 



Old tuberculin is a syrupy brownish-yellow fluid, with a faint 

 aromatic smell. It contains peptones and traces of other proteid 

 bodies, but the nature of the substance on which its extraordinary 

 power depends is quite unknown. It is in a sense to be regarded 

 as a toxin of the tubercle bacillus, but it is not a true toxin, like 

 those of diphtheria and tetanus, since it is practically non-toxic for 

 healthy animals or for man. Its injection in large quantity may 

 cause a slight febrile reaction, but not much more than a similar 

 injection of peptones, etc., from any other source. It differs, also, 

 in a marked degree from the exotoxins in that it is not destroyed 

 by a temperature of 100, or even of 120 C. It is dialyzable. 



When injected into tuberculous animals it causes the same 

 " reaction " as was produced by the living or dead culture, and this 

 in very minute amount. A dose of i milligramme will cause a sharp 

 reaction in a tuberculous patient, and, indeed, one-tenth of that 

 amount will sometimes suffice. When we consider that the 

 material consists mainly of the nutrient ingredients of the broth 

 Koch thought that the active principle might form i per cent, of the 

 whole its extraordinary potency is evident. 



The phenomena of the " reaction " are as follows : There may 

 be, but usually is not, some inflammatory oedema at the seat of 

 injection. The temperature rises precipitously, often reaching 

 105 F. in a few hours, and falls almost as quickly. With this 

 there are the usual symptoms of fever, malaise, shivering, etc. 

 This is the general reaction. The local reaction occurs round the 

 pre-existing tuberculous lesion, and is. best seen in lupus, tubercu- 

 lous ulcers, etc. Its severity depends upon the dose given. With 

 a small dose there is a little redness and swelling and some mild 

 inflammatory oedema, the whole lasting but a day or two. W^hen 

 it subsides the lesion often undergoes great improvement. After 

 larger doses the local reaction is more marked, acute inflammation 

 occurs, the tissues in and around the tuberculous foci undergo 

 coagulation necrosis, and are cast off. When this takes place in 

 the skin it may lead to complete cure, but in the internal organs 

 it is a source of grave danger, often leading to dissemination of the 

 bacilli and a consequent general infection. This occurred in the 



