90 ESSENTIALS OF BACTERIOLOGY 



the colony. This procedure must be carefully done, lest a 

 different colony be disturbed than the one looked at, and an 

 unknown or unwanted germ obtained. 



After the needle has entered the particular colony, it is 

 withdrawn, and the material thus obtained is further exam- 

 ined by staining and animal experimentation. The bacteria 



Fig. 36. Types of stroke cultures: i, Filiform (Bacillus coli); 2, 

 echinulate (Bacterium acidi lactici); 3, beaded (Streptococcus pyogenes); 

 4, effuse (Bacillus vulgaris); 5, arborescent (Bacillus mycoides) (Frost). 



are further cultivated by inoculating fresh gelatin or agar, 

 making stab- and stroke cultures. 



It is necessary to transfer the bacteria to fresh media about 

 every six weeks, as the products of growth and decay given 

 off by the organisms destroy them. Stroke and stab test- 

 tube cultures are more characteristic than plate cultures, as 

 the types in Figs. 35 and 36 show. 



