336 Mr. C. H. Browning and others. Relationships betiveen 



serum ; thus 1 : 2000000 sterilised staphylococci in watery medium, but 

 1 : 1000 failed to kill these organisms in serum. This is the most extreme 

 reduction observed in the case of any substance, being twenty times greater 

 than the reduction effected by serum on mercuric chloride. 



So far, therefore, it has not been possible to obtain any fragment of the 

 molecule which equals, or even approximates closely to, diaminoacridine in 

 antiseptic properties. 



Aeridine Group. 



The substances which have been tested are included in Table II. The 

 following general conclusions may be drawn from the results : — 



Action of the Amino- Groups. — The introduction of amino-groups enhances 

 the antiseptic potency both for Staphylococcus aureus and B. coli, e.g., aeridine 

 [29] and diaminoacridine [35], dimethylacridine [33] and diaminodimethyl- 

 acridine [48]. 



Effectiveness in Serum. — Effectiveness in serum is a characteristic of the 

 compounds with unsubstituted amino-groups and especially of .the metho- 

 chlorides of these bases. The further introduction into the diamino compounds 

 of a phenyl-group attached to the medial carbon atom (in position 9) has, 

 however, a marked effect in diminishing the action in serum ; this is exhibited 

 both in the case of 2 -7-cliamino-3- 6 -dimethylacridine [48 — 51] and 2-amino- 

 3-methylnaphthacridine [58 — 61]. On the other hand, the methochloride of 

 9-phenylacridine [32] is more active than that of aeridine [30]. 



Comparison of the Antiseptic Power of the Methochloride and the Hydro- 

 chloride of the same Base. — The methochloride (or methosulphate or metho- 

 nitrate) is never less potent than the hydrochloride in the presence of serum 

 and in some cases the increased effectiveness shown by the methochloride is 

 very remarkable, e.g., 2-7-tetraethyldiaminoaeridine [55, 56], 2-7-diamino- 

 3-6-dimethyl-9-phenylacridine [50, 51], 2-amino-3-methylnaphthacridine [58, 

 59], 2-dimethylaminonaphthacridine [62, 63]. In the case of the simplest 

 member of the amino series, 2-7-diaminoacridine [35, 36],* and where the 

 substituents are directly attached to the outer rings as in 2-7-diamino- 

 3-6 -dimethylacridine [48, 49], the hydrochloride and the methochloride are 

 practically equal in antiseptic power. It is noteworthy, however, that when 

 the antiseptic power of diaminoacridine is diminished by substitution of ethyl 

 radicals in the amino-groups, the enhanced action of the methochloride [56] 

 over the hydrochloride [55] again becomes apparent. So far, no rational 

 explanation of the enhanced efficacy of the methochloride has suggested itself.f 



* This result has been obtained with carefully purified specimens of these compounds, 

 t The observations of Crum Brown and Fraser on the change produced in the 

 pharmacological action of alkaloids when a methyl group is attached to a nitrogen 



