244 STERILIZATION, ANTISEPSIS AND DISINFECTION 



for an hour daily over a period of five to seven days. The sterilization 

 of Loffler's blood serum in a Koch inspissator is carried out at this 

 lower temperature. 



4. Boiling Water. Petri dishes, culture tubes and other apparatus 

 containing pathogenic bacteria may be freed from bacteria by boiling 

 in water for five minutes. Practically no pathogenic bacteria form 

 spores. If tetanus, anthrax or gas bacillus cultures are to be destroyed, 

 the autoclave is necessary. 



Chemical Solutions. Chemical disinfectants are most efficient in 

 aqueous solutions, and they must therefore be soluble in water. 

 Moisture is also essential for gaseous disinfectants. 



The theory of the germicidal action of disinfectants is not well 

 understood; apparently the efficiency of salts of heavy metals is 

 associated with their noteworthy affinity for proteins, with which they 

 form firm combinations. It must be remembered that these salts 

 react more quickly with animal proteins than bacterial proteins, 

 therefore greater concentrations of metallic salts are required to kill 

 bacteria suspended in protein solutions than to destroy the same 

 organisms in aqueous suspension. Thus, typhoid bacilli may be 

 killed by 1 to 500,000 bichloride of mercury if they are suspended in 

 water, but a concentration of at least 1 to 1500 is required to sterilize 

 the same organism in blood serum. Absolute alcohol does not 

 appear to be a very powerful germicide; possibly its rather limited 

 germicidal value is associated with its dehydrating properties. Dilute 

 solutions of alcohol, 20 to 30 per cent., are practically as destructive 

 of bacteria as absolute alcohol is. Phenols are excellent germicides 

 in aqueous solutions, but their tendency to go into solution in oils 

 (which do not readily penetrate the ectoplasm of cellular structures) 

 makes them unreliable germicides in oily menstrua. 



Salts of Heavy Metals. 1. Mercuric Chloride, HgCl 2 . Mercuric 

 chloride or bichloride of mercury is a powerful germicide, very soluble 

 in hot water, less soluble in cold water. 1 It is usually dispensed in 

 tablet form mixed with NaCl, which increases its solubility and also 

 prevents somewhat its marked tendency to unite with proteins. This 

 is of importance in the treatment of wounds and secretions of wounds 

 with this germicide. A 1 to 1000 solution of bichloride in water is 

 the dilution commonly used for practical purposes. This strength 



1 One part of bichloride will dissolve in 3 to 4 parts of boiling, distilled water; upon 

 cooling, much of the bichloride becomes insoluble; one part of the salt will dissolve in 

 16 to 18 parts of water at room temperature. 



