212 Sterilization and Disinfection 



for good, and may do harm by obscuring odors emanating 

 from harmful materials that should be removed from the 

 room. The practice is only comparable to the old faith in 

 the virtue of asafetida tied in a corner of the handkerchief 

 as a preventive of cholera and smallpox. 



Before one is able to make a scientific application of any 

 germicidal substance it is necessary to become acquainted with 

 its micro-organism-destroying powers. This may seem at 

 first thought to be a simple matter, but is, in reality, one of 

 great complexity and difficulty, for the various micro-organ- 

 isms show marked variations in their powers of endurance; 

 different stages in the development of the micro-organisms 

 show different degrees of resisting power, and the conditions 

 under which the germicide meets the micro-organism effect 

 marked variations in action. These factors make it neces- 

 sary to vary the process of disinfection according to the exact 

 purpose to be achieved. 



Let two examples serve to illustrate these requirements: 

 Bichlorid of mercury is one of the most powerful, reliable, and 

 generally useful germicides, but the strength of its solutions 

 must vary according to the purpose for which they are 

 intended. It kills cocci and non-sporogenic bacilli in dilu- 

 tions of i : 10,000 in from five minutes to twenty-four hours, 

 but to kill anthrax spores requires twenty-four hours' immer- 

 sion in i : 2000 solution. If albuminous substances are 

 present in the medium containing the micro-organisms they 

 precipitate the salt immediately, diminishing the strength of 

 the solution and so retarding or perhaps preventing the 

 germicidal action. Again, certain micro-organisms are de- 

 fended from the action of destructive agents, and among them 

 the germicides, through the presence of waxy matter in their 

 substance. Such is the case with the acid-fast organisms, 

 and notably the tubercle bacillus. Antiformin, a combina- 

 tion composed of equal parts of liquor sodae chlorinatae and 

 a 15 per cent, solution of caustic soda, immediately dis- 

 solves the great majority of micro-organisms, but has no 

 destructive action whatever upon the tubercle bacillus. 



The most useful germicidal substances act destructively 

 upon the micro-organisms by forming chemical compounds 

 with their cytoplasm. Thus, the salts of mercury unite with 

 the protoplasm to form an albuminate of mercury. Other 

 germicidal agents dissolve or coagulate the protoplasm ; still 

 others oxidize and so completely destroy the cells. In the 



