DISINFECTANTS 



97 



3 minutes is necessary. At higher temperatures the 

 efficiency of soaps is considerably increased. Klar- 

 mann and Shternow (1941) however, found that typhoid 

 and dysentery bacteria, as well as streptococci, are 

 not completely killed on infected hands by the cus- 

 tomary use of soaps in lavatories. But their standard 

 of time differs from that of the previously mentioned in- 

 vestigators. 



TABLE 18 



Concentrations (in per cent) of neutral soaps required to kill 

 bacteria. (From Walker, 1925.) 



Walker's results were verified by Tilley and Schaffer 

 (1925) and by Schaffer and Tilley (1930) who, further- 

 more, showed that a slight increase in alkalinity in- 

 creased the germicidal action. The effect of organic 

 matter was studied by adding 50% skim milk which de- 

 creased the efficiency of all soaps greatly. According to 

 Eggerth (1927), serum and other proteins decrease the 

 efficiency of soaps while certain lipoids increase it. 



Schaffer and Tilley (1930) tested also the effect of ad- 

 ditions of phenol, cresol and other disinfectants to soaps 



