f 



PATHOGENIC BACTERIA. 280 



from tuberculous sputum only with very great difficulty. It 

 is best to obtain it from the tissues of an animal that has 

 died of tuberculosis, where the tubercle bacilli may be found 

 unmixed with other bacteria. Pieces of tissue should be 

 taken with the precautions necessary to avoid contamina- 

 tion, 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, 



FIG. 82. 



Bacillus tuberculosis in sputum, stained with fuchsin and methylene blue. 

 Photomicrograph in two colors. (X 1000.) 



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, many will fail to present any 

 growth. After the organism has once been grown upon 

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

 It is best cultivated the first time upon blood-serum. 



