TUBERCLE BACILLUS 445 



cipitated by certain alkaloidal precipitants as tannic acid, potassium 

 mercuric iodide and mercuric chloride in acid solution. It is decom- 

 posed by pepsin HC1 and by trypsin in alkaline media. Proskauer 

 and Beck, 1 and Lowenstein and Pick, 2 and others have shown that 

 tuberculin is produced by the tubercle bacillus when this organism is 

 grown in a protein-free medium. They suggest that it is probably a 

 polypeptid. 



Whether tuberculin contains a true toxin or an endotoxin, or a 

 mixture of both toxin and endotoxin is not clearly settled. Pick 

 believes it contains a true toxin secreted by the tubercle bacillus. 



Variants of Old Tuberculin. A number of observers, impressed with 

 the possibility that the reactive substances of tuberculin might be 

 changed by heat, have attempted to produce tuberculin which has 

 been unheated. 



(a) Bouillon Filtrate Denys (B. F.). This is unheated, uncon- 

 centrated old tuberculin prepared as above and sterilized by passage 

 through sterile porcelain filters. 



(6) Vacuum Tuberculin. The six weeks glycerin broth culture of 

 the tubercle bacillus is concentrated to one-tenth its volume in vacuo 

 and filtered. By so doing the advantages of concentration are 

 obtained without the disadvantages of heating. 



The action of old tuberculin and its variants would suggest that it 

 does not contain all the necessary elements for the establishment of 

 true immunity, and this has led to the production of a series of new 

 products, new tuberculins, which attempt to retain the more specific 

 products of the tubercle bacillus. The principle involved is to grind 

 up dried tubercle bacilli in ball mills to an impalpable powder, and to 

 suspend or partially dissolve this powder in salt solution with or 

 without the addition of glycerin. 



New Tuberculin (T. R. Koch). Young virulent tubercle bacilli are 

 dried first between sheets of sterile filter paper, then in vacuo over 

 sulphuric acid and phosphorus pentoxide until thoroughly anhydrous, 

 then ground in a mortar until a dry powder is obtained. This powder 

 is suspended in water, thoroughly mixed, and then centrifugalized. 

 The first supernatant fluid obtained (T. O.) is rejected. This pre- 

 liminary grinding with water is intended to wash out the water-soluble 

 substance. The residue is then repeatedly ground and centrifugalized, 

 saving the supernatant liquid each time until all of it has passed into 



1 Ztschr. f. Hyg., 1894, xviii, 128. 



2 Biochem. Ztschr., 1911, xiii, 142. 



