CHARACTERS OF CULTURES 



433 



charge of the wound. The isolation of the tetanus bacillus is in 



many cases a difficult matter, and several methods should always 



be tried. ' ; - > ' 



Characters of Cultures. Pure cultures having been obtained, 



sub-cultures can be made in deep upright glucose gelatin or aga/r 



tubes. On deep glucose gelatin (on which 



growth is often very difficult to obtain) there 



commences, an inch or so below the surface, 



a growth consisting of fine straight threads, 



rather longer in the lower than in the upper 



parts of the tube, radiating out from the needle 



track (Fig. 128). Slow liquefaction of the 



gelatin takes place, with slight gas formation. 



In agar the growth is somewhat similar, con- 



sisting of small nodules along the needle track, 



with irregular short offshoots passing out into 



the medium (Fig. 132, A). There is slight 



formation of gas, but, of course, no liquefac- 



tion. On anaerobic agar plates colonies have 



under a low power a feathery outline (Fig. 129). 



Growth also occurs in blood serum and also in 

 glucose bouillon under anaerobic conditions. 



There is in it at first a slight turbidity, and 



later a thin layer of a powdery deposit on the 



walls of the vessel. All the cultures give out 

 a peculiar burnt odour of rather unpleasant 

 character. 



Conditions of Growth, etc. The b. tetani 

 grows best at 37 C. The minimum growth 

 temperature is about 14 C., and below 22 C. 

 growth takes place very slowly. Growth takes 

 place in the absence of oxygen, the organism 

 being an anaerobe. Sporulation may com- 

 mence at the end of twenty-four hours in 

 cultures grown at 37 C., much later at lower 

 temperatures. Like other spores, those of 

 tetanus are extremely resistant. They can 

 usually withstand boiling for five minutes, and can be kept in 

 a dry condition for many months without being killed or losing 

 their virulence. They have also high powers of resistance to 

 antiseptics. 



Pathogenic Effects. The proof that the b. tetani is the cause 

 of tetanus is complete. It can be isolated in pure culture, and 

 when re-injected in pure culture it reproduces the disease. It 

 28 



bacillus in glucose 

 gelatin, showing- 



Natural size. 



