BACILLUS TUBERCULOSIS. 119 



c.c. of such an extract will in tuberculous animals develop 

 marked reactionary symptoms, whereas when used in healthy 

 animals it gives rise to no reaction. 



This tuberculin has a beneficial action in man, especially an 

 action on local tuberculous diseases, such as lupus, tuberculous 

 joints, etc. It is dangerous, however, when used therapeu- 

 tically, because it shows a tendency to stimulate the develop- 

 ment of dormant tuberculosis. 



Recently different forms of tuberculin have been prepared 

 by Koch, known as tuberculin A, O, and R. 



Tuberculin A. This is prepared by extracting the bacilli 

 with decinormal salt solution, and acts very much like ordi- 

 nary tuberculin, being even more severe in effect. 



Tuberculin 0. This is prepared by pounding the dried 

 tubercle bacilli and extracting with distilled water, the 

 emulsion being then passed through the centrifuge. The 

 residue after centrifugation is dried and again pounded and 

 extracted with water, and these processes repeated until no 

 solid residue is left. The whitish liquids from all these 

 operations are mixed, and the result is tuberculin R. 



Tuberculin O is identical in effect to tuberculin A and 

 has an immunizing effect. Tuberculin R gives rise to little 

 reaction, but has a decided immunizing effect. The fluid 

 in tuberculin R is made so that 1 c.c. corresponds to 

 10 milligrams of solid matter, and must be diluted with 

 sterile salt solution to bring it to the required strength. In 

 applying the same therapeutically the dose of tuberculin R 

 for an adult is ^-^ to 1 milligram. It must be used hypo- 

 dermatically, and should be administered every other day. 

 The dose should not give rise to a temperature exceeding 

 1 degree C. 



This produces very satisfactory results in the treatment 

 of lupus, but so far in tuberculous diseases of the lung its 

 effects have not come up to expectation. 



Recently, the tubercle bacillus, on account of its peculiar 

 growth in some cases in which it seems to present projecting proc- 

 esses or branches, has been thought by some to belong to the 



