2 7 6 



PATHOGENIC BACTERIA. 



great majority of the spores except those of tetanus, were 

 destroyed, aud, as little other than tetanus spores re- 

 mained, their cultivation was made comparatively easy. 

 The resistance which the tetanus bacilli manifest toward 

 heat is only part of a great general resisting power of 

 which they are possessed. It is said that they can retain 

 their vitality in the dried condition for months. Stern- 

 berg says they can resist 5 per cent, carbolic solutions 

 for ten hours, but will not grow after fifteen hours' im- 

 mersion. 5 per cent, carbolic acid, to which 0.5 per cent. 



FIG. 75. Bacillus tetani : five-days-old colony upon gelatin containing glucose ; 

 x IOOO (FrS.nkel and Pfeiffer). 



of hydrochloric acid has been added, destroys them in 

 two hours. They are also destroyed in three hours by 

 i : looo bichlorid-of-mercury solution ; but when to such 

 a solution 0.5 per cent, of hydrochloric acid is added, its 

 activity is so increased that the spores are destroyed in 

 thirty minutes. The resistance to heat is only within 

 certain limits, for exposure to passing steam for from 

 five to eight minutes is certain to kill the spores. 

 The colonies of the tetanus bacillus, when grown in 



