176 Sterilization and Disinfection 



atmosphere of a room during its occupancy by the patient. It is 

 entirely useless to place beneath the bed or in the corner of a room 

 small receptacles filled with carbolic acid or chlorinated lime. These 

 can serve no purpose 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 asaf etida tied in a corner of the handkerchief as a preventive 

 of cholera and smallpox. 



DISINFECTANTS 



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-organisms 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 necessary 

 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 dilutions of i : 10,000 in .from five minutes to 

 twenty-four hours, but to kill anthrax spores requires twenty-four 

 hours' immersion in i : 2000 solution. If albuminous substances are 

 present in the medium containing the micro-organisms they precipi- 

 tate the salt immediately, diminishing the strength of the solution 

 and so retarding or perhaps preventing the germicidal action. Again, 

 certain micro-organisms are defended 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 com- 

 bination composed of equal parts of liquor sodas chlorinatae and a 

 15 per cent, solution of caustic soda, immediately dissolves the 

 great majority of micro-organisms, but has no destructive action 

 upon the tubercle bacillus. 



The most useful germicidal substances act destructively upon the 

 micro-organisms by forming chemical compounds with their cyto- 

 plasm. 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 process of germicidal action many and 

 varied activities are at work, and, as all are not understood, the 

 subject is a difficult one to handle in a limited amount of space. 



