TUBERCLE BACILLUS. 577 



by various means. Its prolonged existence in putrid 

 sputum decreases its virulence and a similar de- 

 crease occurs on potato, in old cultures or in those 

 which contain iodoform, boracic acid and some 

 other substances. Inoculation with such cultures 

 produces a chronic form of tuberculosis in animals 

 which may heal. In other instances cultures which 

 have grown on artificial media for many years re- 

 tained their original virulence. 



The organism contains about 90 per cent, of 

 water. One-fourth of a dried bacterial mass may 

 be extracted as a wax-like or fat-like substance by 

 a mixture of alcohol and ether. The acid-fast 

 staining property of the bacillus depends on this 

 substance. The remaining portion of the mass, 

 consisting largely of proteins, which may be ex- 

 tracted by dilute alkalies, contains a toxic nucleo- 

 albumin. Cellulose, representing a portion of the 

 capsular substance, is also found in the residue. 



Killed cultures when given subcutaneously pro- Toxic 

 duce necrosis, abscesses, caseation, marasmus, and * 

 a subnormal temperature. When given to rabbits 

 and guinea-pigs intravenously they cause rapid 

 emaciation and death in from a few days to a few 

 weeks. By beginning with very minute doses, how- 

 ever, the animals may be gradually habituated to 

 intoxication by the dead bacilli and eventually 

 withstand large doses. The same holds true of the 

 various toxic substances, including tuberculin, 

 which may be extracted from cultures. The pro- 

 teins and alkaline extracts cause abscesses when 

 given subcutaneously. The fever-producing sub- 

 stance which is present in the preparations men- 

 tioned below is one of the metabolic products of 

 the bacillus, rather than a constituent of the bac- 



