136 ANTISEPTICS AND DISINFECTANTS 



Another method is to make bouillon cultures of an organism and 

 add to each a certain percentage of the solution of the antiseptic, 

 and abstract every few minutes after the addition of the chemical 

 one loopful of the mixture and inoculate fresh media. 



Pieces of thread sterilized, and then put in fluid cultures may 

 be used in experiments; they are dipped into solutions of chemicals 

 for varying lengths of time and then placed in culture media 

 and growth noted. 



It will be found in the case of most antiseptics in dilute solution 

 that an interval of time must elapse before the organisms are 

 killed. This is determined by observing the cultures made from 

 the mixture. After five minutes, growth may occur, but after 

 one hour, all may be dead, or it may take two or three hours. 



The student should refer to works on hygiene for standard 

 methods of controlling disinfectants, for example the Hygienic 

 Laboratory and the Rideal- Walker methods. 



The most valuable chemical disinfectants are those that kill in 

 highly dilute solution in a short time. 



Bichloride of mercury is a highly efficient germicide in watery 

 solutions; if, however, albuminous matter is present its action is 

 inhibited very much. 



CHEMICAL DISINFECTANTS 



Mercury Salts. Bichloride of mercury in highly dilute solution 

 is a very valuable antiseptic. It dissolves in 16 parts of tepid 

 water. It requires an acid reaction for most favorable action 

 and the tablets now on the market are made up with some acid 

 having no effect upon the mercury salt. In i-ioo water solution 

 this salt will kill anthrax spores in twenty minutes. In blood, 

 the anthrax bacillus is killed by a 1-2,000 solution in a few minutes. 

 In bouillon the same organism is killed in a dilution of 1-40,000; 

 in water, 1-500,000; all in the same interval of time. The pres- 

 ence of the albumins in the blood or bouillon, no doubt acts as a 



