PATHOGENIC BACTERIA. 353 



tubercle bacilli may be found unmixed with other bacteria. 

 Pieces of tissue should be taken with the precautions necessary 

 to avoid contamination, and should be broken up and rubbed 

 over the surface of the medium. The tubes must be closed 

 with sealing-wax, paraffin or rubber stoppers, or covered with 

 rubber caps, to prevent drying in the incubator. If rubber 

 caps are used, they should first be left in i-iooo bichloride of 

 mercury for an hour, and the cotton plug should be burned 

 before putting on the rubber cap. A number of tubes should 

 be inoculated, using rather large particles of the tuberculous 

 material. Among the tubes inoculated, some are apt to show 

 no growth. After the organism has once been grown upon 

 a culture-medium it may be propagated with less difficulty. 



The statement in regard to the action of germicidal agents in 

 general may be repeated here with regard to their action upon 

 the tubercle bacillus. The results of laboratory experiments 

 to determine the effects of the various agents upon the tubercle 

 bacillus cannot with safety be absolutely relied upon in practice 

 to destroy the bacilli. The measures employed in practice 

 should in all cases be much more drastic than would be 

 indicated as just sufficient by the results of laboratory experi- 

 ments. Absolute destruction by fire should be resorted to 

 whenever this is feasible, and next to this sterilization in the 

 autoclave at 115 to 120 C. Chemical disinfectants are 

 uncertain, particularly in the disinfection of sputum, feces 

 and the like. The following statements in regard to the 

 effects of various germicides are, therefore, of more theoretical 

 than of practical interest. 



The bacilli are very resistant to drying. They remain alive 

 for about two months when kept dry. They are also more 

 resistant to the destructive action of heat when dry than when 

 moist. They have been known to remain alive after one hour's 

 heating at 100 C. when dry; but when they are exposed in 

 water, milk, beef-broth or other fluids they are killed at 55 C. 



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