3l6 SPECIFIC MICRO-ORGANISMS 



pig tissue, about four weeks later.^ 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 incubating 

 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 



Fig. 130. — Tubercle bacillus showing branching and involution forms. {After 



Migula.) 



glycerin potato are usually successful. Old 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 phosphoric 

 acid (PO4). The waxy constituent of the bacterial cells is of 



' It is possible to cultivate tubercle bacilli directly from contaminated material 

 such as sputuin, by careful technic, although the results are somewhat uncertain.- 

 A method is described in detail by Williams, W. W. and Burdick, Journal of Bact.^ 

 1916, I, p. 411-414. 



