538 BACTERIOLOGY. 



colonies the entire mass is made up of a number of 

 distinct threads that give it the appearance of a com- 

 mon mould. (See Fig. 87.) 



In stab-cultures made in tubes about three-quarters 

 filled with gelatin growth begins at about 1.5 to 3 cm. 

 below the surface, and gradually assumes the appearance 

 of a cloudy, linear mass, with prolongations radiating 

 into the gelatin from all sides. Liquefaction with coinci- 

 dent gas-production results, and may reach almost to 

 the surface of the gelatin. 



RELATION TO TEMPERATURE AND TO CHEMICAL 

 AGENTS. It grows best at a temperature of from 

 36 to 38 C. ; gelatin cultures kept at from 20 to 

 25 C. begin to grow after three or four days. In an 

 atmosphere of hydrogen at from 18 to 20 C. growth 

 does not usually occur before one week. No growth 

 occurs below 14 C. At the temperature of the body 

 spores are formed in cultures in about thirty hours, 

 whereas in gelatin cultures at from 20 to 25 C. they 

 do not usually appear before a week, when the lower 

 part of the gelatin is quite fluid. 



Spores of the tetanus bacillus when dried upon bits 

 of thread over sulphuric acid in the desiccator and sub- 

 sequently kept exposed to the air, retain their vitality 

 and virulence for a number of months. Their vitality 

 is not destroyed by an exposure of one hour to 80 C. ; 

 on the other hand, an exposure of five minutes to 

 100 C. in the steam sterilizer kills them. They resist 

 the action of 5 per cent, carbolic acid for ten hours, but 

 succumb when exposed to it for fifteen hours. In the 

 same solution, plus 0.5 per cent, of hydrochloric acid, 

 they are no longer active after two hours. They are 

 killed when acted upon for three hours by corrosive 



