248 AIDS TO BACTERIOLOGY 



Delepine defines an ' antelethal inhibitory period ' 

 existing before actual death. He also shows that some 

 disinfectants, when dilution is pressed beyond the 

 ' ultimate lethal dilution,' actually excite growth of 

 bacteria. 



Gossl found some disinfectants to owe their efficiency 

 towards yeast cells to the fact that they are soluble in 

 the cell-lipoids. 



Behaviour of Chemical Disinfectants. In oil or alcohol 

 disinfectants lose all or most of their activity. The value 

 of alcohol itself as a disinfectant is also lessened when it 

 holds other things in solution, but tincture of iodine is 

 an exception. Among fats, lanolin alone seems com- 

 patible with the disinfectant efficiency of substances 

 exhibited in it, probably because it holds them in a fine 

 emulsion of their watery solutions (Gottstein). Some 

 disinfectants form an emulsion on the addition of water. 

 Rideal and Walker found that a resin soap emulsion of 

 tricresol had three times the germicidal value of an oleate 

 solution of the same disinfectant. 



The temperature at which the organism is exposed to 

 the disinfectant has a considerable influence on the extent 

 or rate of disinfection. Up to the optimum temperature 

 at whicl> the organism to be disinfected grows on the 

 medium in which it is exposed, the activity of a disinfectant 

 may fall off as the temperature rises, owing to the increased 

 vigour which the organism derives from the improvement 

 in its conditions in respect of temperature. On the con- 

 trary, as cooling below the optimum temperature proceeds, 

 the organism gradually passes into what Christian calls 

 ' a state of coma,' where the bacterial cell has a corre- 

 spondingly low tendency to undergo chemical change. 

 In practice, the latter alternative seems more frequent 

 that is, diminution in temperature lessens disinfectant 

 action. A relatively small difference of temperature 

 two or three degrees may make an appreciable differ- 

 ence in the activity of disinfectants, and in their examina- 

 tion failure to remember this has led to serious error. 

 Above the optimum a rise of temperature increases the 

 activity of the disinfectant, sometimes to an enormous 

 extent. 



Fasson, Ponder, and Sims Woodhead, comparing 

 emulsified disinfectants (cresols, etc.) with carbolic acid, 



