302 



SPECIFIC MICRO-ORGANISMS 



pig tissue, about four weeks later. 1 The tubes may be sealed 

 with rubber caps or paraffin and incubated at 37 C. Better 

 results are obtained by leaving the tubes unsealed and in- 

 cubating at 37 C. in an atmosphere saturated with moisture, 

 as the bacillus is a strict aerobe, but this requires special care 

 and is not absolutely essential to success. After two or three 

 weeks a dry, white growth is developed which may later become 

 folded. Transplants from the primary culture to glycerin agar, 

 glycerin broth or glycerin potato are usually successful. Old 



FIG. 127. Tubercle bacillus showing branching andjinvolution forms. (After 



Migula.} 



cultures on potato and agar often become yellowish or even 

 pink in color. 



The chemical composition of tubercle bacilli has been ex- 

 tensively studied. The moisture content varies from 83 to 89 

 per cent. The ash (inorganic salts) amounts to about 2.6 per 

 cent of the dry substance, and about half of this is phosphor c 



1 It is possible to cultivate tubercle bacilli directly from contaminated material, 

 such as sputum, by carefully washing it in sterile water and then spreading it over 

 the surfaces of a series of serum tubes. Results are somewhat uncertain. For 

 details of this and other methods see Kolle and Wassermann, Handbuch, 1912, 

 Bd. V, S. 420-422. 



