88 DISINFECTANTS 



and no suggestions have been made concerning their mode 

 of action. 



The only other heavy metal compounds used extensive- 

 ly as disinfectants are those of silver. The silver salts, 

 nitrate, lactate, and citrate, act probably through their 

 metallic ion, as in the case of the mercury salts. Their 

 instantaneous reaction with chlorides to form insoluble 

 AgCl limits their usefulness greatly. 



The preparations of silver metal in colloidal form, with 

 trade names like argyn, argyrol, solargentum, silvol, etc., 

 are of particular interest. Metallic silver does not react 

 with chlorides or proteins as silver ions do, but it is only 

 a very weak disinfectant. According to Leonard (1931), 

 a suspension containing as much as 1 gram of colloidal 

 silver in 100 cc. does not kill the test organisms Bact. 

 coll and Staph, aureus, though suspensions of 1 gram in 

 10,000 are sufficient to prevent multiplication. 



This leads us to the problem of the oligodynamic action 

 of metals which is still much debated. The first obser- 

 vations were made with metallic copper whose disin- 

 fecting action has been proved by several investigators. 

 The lethal effect cannot be due to copper ions going 

 into solution from the metal because the solubility of 

 metals is immeasurably small, and a corresponding 

 amount of copper ions from any copper salt has not the 

 least inhibiting effect. Even a solution of 5% copper 

 chloride does not kill Staphylococcus aureus in one hour. 



If direct contact of the cells with the metal were nec- 

 essary to bring about death, the latter might be explained 

 by a chemical combination of some essential cell con- 

 stituent with the metal, or by a physical action, such as 

 interference with some electric potential in the cell. 

 However, no conclusive proof has been given that direct 

 contact is necessary. 



Most experimenters agree that oxygen is necessary 

 to bring about the lethal effect of metallic copper sur- 



