DISINFECTION. 



415 



DISTINCT RETARDATION 

 OF GROWTH 



COMPLETE CESSATION 

 OF GROWTH 



ON ADDITION OF 



More than 



1500 

 1700 

 1250 

 700 



800 

 850 

 625 



I : 12.5 



From the foregoing it will appear that even quite slight 

 additions of the disinfectant may nullify the results of the 

 experiment when the method of investigation first named 

 of introducing the silk threads into the nutrient medium is 

 pursued. When Geppert, by means of dilute solutions of 

 ammonium sulphate, removed completely the disinfectant 

 from the anthrax-spores that had lain in mercuric-chlorid 

 solution, I : 1000, before their transference to the nutrient 

 medium, he still observed growth after exposure to the 

 action of the mercuric chlorid for fifteen minutes, and also 

 after exposure for five hours, and in one instance even after 

 exposure for twenty-four hours. The spores were still 

 infective. Animals that Geppert inoculated therewith fre- 

 quently died of anthrax. Solutions of mercuric chlorid of 

 i : 100 did not with certainty destroy the spores in from 

 six to twelve minutes. From this it can be seen that the 

 disinfecting activity of the agents tested by the method of 

 Koch has probably been often placed too high. The 

 figures obtained by Koch and numerous subsequent investi- 

 gators still retain their value for practical purposes, as Koch 

 himself endeavored to reduce to a minimum the sources 

 of error indicated by making the silk threads as short, 

 and using as large an amount of culture-medium, as 

 possible, and rinsing in distilled water, alcohol, etc., the 

 threads removed from the antiseptic solution before trans- 

 ference to the nutrient solution. 



The following table from Fliigge's " Text -book " (1897) 



