96 DISINFECTANTS 



concentrations occasionally differing a hundredfold be- 

 tween strains of the same species (Tilley and Schaffer, 

 1930). 



Walker (1924) began to unravel this problem by 

 studying first the efficiency of the potassium and sodium 

 salts of each fatty acid; later (1925) he investigated the 

 various soaps from different fats and oils. Outstanding 

 among the components studied was Na or K laurate 

 which killed pneumococci and streptococci in high dilu- 

 tions, and also affected typhoid bacteria, but had no 

 action on a strain of Staphylococcus aureus which was 

 completely resistant to all soaps. Klarmann (1933) ver- 

 ified the exceptionall}'^ strong effect of lauric acid. 



Later, in 1941, Klarmann and Shternow found capric 

 acid more efficient than lauric. Myristic acid was weaker, 

 though more jDowerful than palmitic. This held true for 

 all bacteria tested except for typhoid and dysentery bac- 

 teria for which palmitic and stearic acids were as toxic 

 as lauric and myristic. 



The salts of unsaturated acids (oleic, linolic and lino- 

 lenic) are highly bactericidal for pneumococci and strep- 

 tococci, but entirely harmless for typhoid bacteria. So- 

 dium ricinoleate has a marked selective action, which is 

 utilized in the isolation of the colon-typhoid group. 



Walker (1925) investigated commercial soaps as well 

 as some he made himself from pure fats. He too found 

 the coconut oil soap, which contains much lauric and my- 

 ristic acid, superior to all others in killing streptococci 

 and typhoid bacteria (Table 18). In hand-washing, the 

 soap concentration varies from 0.3% in hasty rinsing to 

 15% in prolonged scrubbing of the hands, and can be 

 considered to average about 8% when the hands are wash- 

 ed thoroughly with the purpose of cleaning them. Thus, 

 while any ordinary soap is sufficient to destroy any ad- 

 hering streptococci, pneumococci. and diphtheria bacte- 

 ria, for typhoid bacteria, coconut oil soap acting for 



