The Germicidal Value 247 



precaution as regards asepsis, after sterilization and imme- 

 diately before the test is made. Control experiments i. e., 

 bouillon cultures without the addition of the antiseptic 

 should always be made. 



The results of antiseptic action are two: retardation of 

 growth and complete inhibition of growth. As the inoculated 

 tubes containing the antiseptic are watched in their devel- 

 opment, it will usually be observed that those containing 

 very small quantities develop almost as rapidly as the control 

 tubes; those containing more, a little more slowly; those 

 containing still more, very slowly, until at last there comes a 

 time when the growth is entirely checked. 



Sternberg points out that the following conditions, which 

 must be avoided, may modify the results of experiment : 



1 . The composition of the nutrient media, with which the 

 antiseptic may be incompatible (as bichloride of mercury 

 and albumin). 



2. The nature of the test-organism, no two organisms 

 being exactly alike in their susceptibility. 



3. The temperature at which the experiment is conducted, 

 a relatively greater amount of the antiseptic being necessary 

 at temperatures favorable to the organism than at tempera- 

 tures unfavorable. 



4. The presence of spores which are always more resistant 

 than the asporogenous forms. 



II. The Germicidal Value. Koch's original method of 

 determining this was to dry the micro-organisms upon sterile 

 threads of linen or silk, and then soak them for varying lengths 

 of time in the germicidal solution. After the bath in the 

 reagent the threads were washed in clean, sterile water, 

 transferred to fresh culture media, and their growth or fail- 

 ure to grow observed. This method also determines the 

 time in which a certain solution will kill micro-organisms, so 

 is advantageous. 



Sternberg suggested a method by which the dilution nec- 

 essary to kill the bacteria could be determined, the time 

 remaining constant (two hours' exposure) in all cases. 

 " Instead of subjecting test-organisms to the action of the 

 disinfecting agent attached to a silk thread, a certain quan- 

 tity of a recent culture usually 5 c.c. is mixed with an 

 equal quantity of a standard solution of the germicidal 

 agent, . . . and after two hours' contact one or two 

 loopfuls are transferred to a suitable nutrient medium to 

 test the question of disinfection." 



