130 TUBERCULOSIS. 



are not affected by small doses of tuberculin, whereas animals 

 that have the least tuberculous taint will show decided reac- 

 tion when injected with tuberculin. This procedure is used 

 extensively in all civilized countries nowadays for the diag- 

 nosis of tuberculosis in cattle and other animals. 



The original tuberculin of Koch is prepared from an extract 

 of glycerin-bouillon of virulent bacteria, in which the bacteria 

 themselves are quickly killed by exposure to a higher tem- 

 perature, and filtered away by a Chamberlain filter. 0.025 

 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, called old 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 therapeutically, because it shows a tendency to 

 stimulate the development of dormant tuberculosis. 



Recently different forms of tuberculin have been prepared by 

 Koch, known as tuberculin A, O, and R (new tuberculin). 



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. 



