252 



Value of Antiseptics 



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 anti- 

 septic may be incompatible (as bichloride of mercury and albumin). 



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

 actly alike in their susceptibility. 



3. The temperature at which the experiment is conducted, a 



C 



Same rod immersed in broth after 

 exposure to disinfectant. 



Fig. 87. Glass rod in test-tube, for use in testing disinfectants. Tube 

 6 in. by % in.; rod 9 in. by y in. Ring marked with diamond i in. from lower 

 end, to show upper limit of area on which the organisms are dried. After ex- 

 posure the rod is placed in a similar tube containing broth, to test development, 

 a, Cotton plug wrapped around glass rod; b, broth; c, gummed label on handle 

 of rod, for identification; d, ring marked by diamond; e, dried organisms. 



relatively greater amount of the antiseptic being necessary at tem- 

 peratures favorable to the organism than at temperatures unfavorable. 



4. The presence of spores which are always more resistant than the 

 asporogenous forms. 



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

 ing 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 germi- 

 cidal solution. After the bath in the reagent the threads were washed 

 in clean, sterile water, transferred to fresh culture-media, and their 



