ANTISEPTICS 127 



Gram staining and sensitivity to penicillin (and this has 

 been quite useful as a guide to medical application). 

 However, there are striking exceptions, such as equal 

 sensitivity of Streptococcus viridans and Proteus, or the 

 extreme sensitivity of the Gram-negative Neisseria gon- 

 orrhoeae. Typical exceptions, even if few, are enough 

 to disprove the assumption that Gram staining and sus- 

 ceptibility to penicillin are fundamentally of the same 

 origin. 



Another frequently made claim is that the basic dyes 

 inhibit Gram-positive bacteria far more than Gram-neg- 

 ative. Ingraham (1933) investigated 20 species and ar- 

 ranged them in the order of their sensitivity to gentian 

 violet (measured by a quantitative index). In her list 

 the most sensitive genera were the Gram-positive Bacillus, 

 Streptococcus and Staphylococcus; but among the most 

 tolerant organisms were two species of Clostridium, 

 which are usually considered Gram-positive. However, 

 since both species are Gram-positive only when young, 

 and become Gram-negative with age, this observation 

 can not be considered as an argument against the gen- 

 eral claim (see, however, the Chapter on Dyes). 



Cooper and Mason (1927) studied the differences in 

 the two outstanding Gram-negative groups, Bacterium 

 coll and Pseudomonas. They came to the conclusion that 

 the Pseudomonas group was very sensitive to such 

 agents as heat or alcohol which produce physico-chemi- 

 cal changes of the colloidal state or denaturation of the 

 protoplasm, but rather resistant to substances which re- 

 act chemically, while the colon group showed the oppo- 

 site characters. They determined the lowest concentra- 

 tions inhibiting multiplication for 48 hours. With most 

 reagents Pseudomonas putida, the most sensitive species 

 of that genus, was more easily inhibited than Bacterium 

 coli; but the differences in sensitivity were slight except 

 with quinol and pyrogallol, of which Bacterium coli could 

 tolerate more than twice as much as Pseudomonas. With 



