610 APPLICATION OF METHODS OF BACTERIOLOGY 



dense, felt-like center surrounded by a fringe of delicate 

 radii. The liquefaction is so slow that the appearance is 

 retained for a relatively long time, but eventually becomes 

 altered. In very old colonies the entire mass is made 

 up of a number of distinct threads that give it the ap- 

 pearance of a common mould. (See Fig. 101.) 



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 coincident 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 subse- 

 quently 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 cent, of hydrochloric acid, they are no longer active after 



