186 PRINCIPLES OF DISINFECTION 



flaming the mouth, is poured into a flask containing 100 c.c. of 

 sterile bouillon. The flasks are incubated for forty-eight hours and 

 solid media are inoculated from these. By this method even a single 

 surviving bacterium is given an opportunity for subsequent develop- 

 ment. The effect of sunlight and other physical influences may be 

 ascertained in an identical manner. 



Testing the Effect of Chemical Disinfectants or Antiseptics. The 

 method generally employed is the following: Sterile silk threads are 

 soaked in culture media containing the bacteria whose resistance is 

 to be tested. The threads are afterward dried and suspended for 

 different periods of time in solutions of varying strength of the anti- 

 septic. The latter is then washed off in sterile distilled water and 

 the silk threads are immersed in fluid or liquefied solid culture media. 

 Since there are certain objectionable features in the silk-thread 

 method it has been modified, and small sterile garnet crystals on 

 which the bacteria are dried are used to replace the threads. The 

 crystals are treated in the same manner as the threads. All chemical 

 disinfectants act more quickly at high than at low temperatures; that 

 is at high temperatures which are not in themselves damaging. This 

 observation corresponds with the general law that chemical reactions 

 take place more promptly and more rapidly at higher temperatures. 



Dry and Moist Heat. One of the most important considerations in 

 the study of heat in disinfection is the fact that dry heat is very 

 much less effective than moist heat. This is particularly apparent 

 in the case of spores. Anthrax spores, for instance, can withstand 

 dry heat at 100 to 120 C. for several hours, and even at 140 C. their 

 absolute destruction is only accomplished after three hours, while 

 water boiling at 100 C. kills them, even at the highest estimate, in 

 twelve minutes. The effect of steam developed under pressure in 

 the autoclave is still more powerful. The spores of certain soil and 

 potato bacilli can withstand streaming steam at 100 C. for over 

 sixteen hours, but they are killed in steam under pressure at 105 to 

 110 C. in from five to fifteen minutes and at 140 C. in one minute. 

 Steam developed under reduced pressure at a lower temperature, as 

 at high altitudes or in experimental work is, of course, less effective 

 in killing spores than steam at the ordinary pressure of one atmos- 

 phere and at 100 C. Overheated steam not saturating the atmos- 

 phere in which the spores are exposed also has a reduced destructive 

 power. Esmarch and Kokubo found that a very small admixture of 

 antiseptics, (creosote, formalin, etc.) to the streaming steam, enor- 

 mously increased its destructive power toward spores. Dry heat is 

 not only much less powerful as a disinfectant than moist heat, but is 

 also relatively of much less value because it has little penetrating 

 power. Koch and Wolffhiigel showed experimentally that in a bale 

 composed of nineteen woollen blankets, which had been exposed for 

 three hours to dry heat of 130 to 140 C., the temperature in the 

 interior had only risen to 35 C. 



