Antiseptic Action and Chemical Constitution. 331 



in the pyridine or quinoline nucleus, reinforced by one or more amino groups. 

 It is for this reason that substances of this type were first examined. 



In addition, a series of acridine derivatives have been prepared and tested 

 for their antiseptic power in order to determine, if possible, whether any 

 law could be established relating chemical structure and antiseptic 

 action within the group. Also, observations have been made upon 

 phenazine compounds, on account of their close chemical relationship to the 

 acridine group. 



Methods of Estimating Antiseptic Power. 



The substance to be tested, in a volume not exceeding 0*1 c.c, was added 

 to 1 c.c. of the culture medium, which consisted : (a) of a watery solution 

 containing - 35 per cent, sodium chloride, and 0*7 per cent, bacteriological 

 peptone, such as Witte's, the hydrogen-ion concentration of the mixture 

 being adjusted by the addition of caustic soda to yield a Ph value between 

 7*2 and 7'8 as indicated by the usual indicators ; and (b) sterile ox serum, 

 which had been previously heated for several hours at 56° C, in order to 

 destroy normal bactericidal power as well as accidental contaminating 

 organisms. Serum, in virtue of its content in protein, has a powerful action 

 in reducing the bactericidal effect of most strong antiseptics, at the same 

 time it represents the fluid constituent to which antiseptics in contact with 

 the tissues are exposed, e.g., in a surgically treated wound ; serum also acts 

 as a satisfactory culture medium for the two types of organisms employed, 

 and is extremely constant in composition and reaction. Hence, serum may 

 be regarded as a highly suitable medium in which to test antiseptic action. 

 The organisms employed in the tests were Staphylococcus aureus and a 

 single strain of B. coli; the inoculation dose being 01 c.c. of a 1:1000 

 dilution in saline of a 24 hours' culture in peptone water. Experiments 

 have shown that within wide limits the efficiency of the antiseptic, as 

 tested by the method described, is practically independent of the size of the 

 inoculum (3, 8). But inoculation with very large numbers of organisms should 

 be avoided, as these fail to maintain themselves in the medium even in the 

 absence of any antiseptic (3). In general, the following series of concentra- 

 tions of each substance was tested, 1 : 1000000, 1 : 400000, 1 : 200000, 

 1 : 100000, 1 : 40000, 1 : 20000, 1 : 10000, 1 : 4000, 1 : 2000, 1 : 1000. Thus, 

 in examining any given compound, the effect of varying concentrations was 

 tested at the same time and with the same batch of medium and the same 

 cultures of organisms. The mixtures were incubated at 37° C. for 48 hours, 

 and then the final readings were made ; the occurrence of abundant growth 

 was shown by the development of turbidity in the previously clear medium, 

 but subcultures frequently yielded growth from tubes which appeared to be 



