STERILISATION. 25 



chemicals. More recently the knowledge of antiseptics has 

 been greatly extended by R. Koch. As in the case of the 

 action of heat, so the individual species react differently towards 

 the various antiseptics. Moreover, one and the same species 

 of vegetation may react differently towards the same reagent, 

 and that not only because the spores possess a greater power 

 of resistance than the vegetative cells, but also because the 

 activity of the latter plays a part. One practical problem 

 is to determine how far the antiseptic can be diluted without 

 ceasing to react. Whilst with a given concentration the 

 antiseptic may prohibit life, with a greater dilution the action 

 only restricts development, and with still greater dilution, if 

 any further influence is felt, it may take the form of stimulating 

 both the development and activity of the organism. Many 

 organisms possess a special power of accommodating them- 

 selves to strong doses of antiseptics. 



Disinfectants are placed on the market either in a solid or 

 in a concentrated liquid condition. Their antiseptic power 

 must first be determined by experimenting with the groups of 

 micro-organisms which may be encountered in the fermentation 

 industry. Once the limit of their activity is determined, it- 

 is necessary to ascertain how rapidly a given dose operates. 

 Should it prove that the action is too slow for practical appli- 

 cation, other degrees of dilution must be tested until the 

 minimum dose is found which will kill the micro-organisms 

 in a short time (e.g., in thirty minutes). 



Flasks of 15 c.c. capacity, provided with ground glass 

 stoppers, are used for the test. These are filled almost to the 

 top with the disinfectant, and after a pure culture of each 

 species has been placed in the flasks, they are thoroughly 

 shaken. 



When the action is completed, every trace of the reagent 

 must be removed from the vegetation by washing, and a sample 

 of the growth is transferred to a suitable nutritive substratum, 

 and exposed under the most favourable conditions. It must 

 be maintained at a constant temperature, which should be 

 higher than that of the room. Liquids are to be preferred 

 to gelatine, because the nutritive value of the latter is generally 

 smaller. Finally, the observation of such growths must 



