PHYSIOLOGY OF MICROORGANISMS 53 



the protoplasm, by dissolving or coagulating the protoplasm, or by 

 oxidation and complete destruction of the cells. Our most efficient 

 disinfectants are those which destroy in the manner first named. 

 The activity and efficiency of many disinfectants depend upon 

 the ionization of the compound in solution. This is particularly 

 true with the salts of heavy metals, such as mercuric chlorid 

 (corrosive sublimate). It is the ionized mercury that is poison- 

 ous to bacteria. Mercuric chlorid does not ionize in pure alcohol, 

 hence it is not poisonous to bacteria when in solution in that 

 substance. The addition of various other chemicals may increase 

 or decrease the ionization of the disinfectant and enhance or dimin- 

 ish its destructive action. 



Disinfectants and Antiseptics in Common Use. Salts of the 

 Heavy Metals. The salts of gold, silver, copper, and mercury 

 are all active disinfectants. Copper sulphate is sometimes 

 used in an effort to free water reservoirs and other city supplies 

 from growths of objectionable algae. Mercury is the most efficient 

 of the metals and its salts are most commonly used. It acts by 

 forming a mercuric, albuminate of the protoplasm. When used 

 in any solution containing considerable quantities of protein or 

 similar materials, as in feces, it must be used in excess and thor- 

 oughly mixed, for it is apt to form an insoluble coating over the 

 surface of the solid particles and protect the bacteria in the interior 

 from destruction. Mercuric chlorid is usually used in solutions 

 of 1 : 1000 or 1 : 2000. 



Lime, unslaked, is a fairly efficient disinfectant. It is par- 

 ticularly useful because in the form of whitewash it may be 

 applied as a permanent coating to the walls of stables and out- 

 buildings. Feces and urine may be disinfected by a mixture 

 of equal parts of a 20 per cent, solution of freshly slaked lime 

 with the material to be disinfected. 



Phenol, or carbolic acid, C 6 H 5 OH, and the methyl phenols or 

 cresols, CsFLCHaOH, either pure or in the trade mixtures, such 

 as kreso, tricresol, creolin, etc., are among the most efficient 

 and useful of disinfectants. They are most frequently used in 

 1 to 5 per cent, solutions, and will destroy bacteria even in the 

 presence of quantities of organic matter. 



Sulphur Dioxid and Sulphurous Add. When sulphur is 



