The Effect of Chemicals on Microorganisms • 201 



SPECIFIC COMPOUNDS EMPLOYED AS DISINFECTANTS 



HEAVY METALS 

 When metals were first considered as possible agents in disin- 

 fection, their activity was referred to as an oligodynamic action 

 (oligOy small; dynamic, powerful), because a small amount of metal 

 appeared to exert a highly lethal effect on microorganisms. The 

 salts of silver and of mercury represent two of the better known 



Fig. 34. Oligodynamic action of silver. Note the absence of growth 

 in the area immediately surrounding the dime in a pour plate of 

 Escherichia coli. (By permission from Introduction to the Bacteria by 

 C. E. Clifton. Copyriglit, 1950. McGraiv-Hill Book Compamj, Inc.) 



compounds employed as disinfectants. Recent evidence, however, 

 points to the fact that these salts act more as bacteriostats than as 

 bactericides. 



1. Bichloride of Mercury (HgCL) is commonly used in a con- 

 centration of 1:500 or 1:1000 as a disinfectant, with higher dilu- 

 tions acting as bacteriostats. As effective as this compound ap- 

 pears to be, it has several disadvantages which limit its usefulness. 

 It is highly corrosive; in fact, it is commonly referred to as corro- 

 sive sublimate. The compound is poisonous to man and to ani- 

 mals, and it does cause coagulation of proteins. This latter feature 

 explains why, when someone swallows bichloride of mercury, 



