THE ACTION OF ANTISEPTICS 169 



animal or vegetable body is more or less harmful to bacterial 

 life, yet certain bodies have a more marked action than others. 

 Thus it may be said that the most important antiseptics are the 

 salts of the heavy metals, certain acids, especially mineral acids, 

 certain oxidising and reducing agents, a great variety of sub- 

 stances belonging to the aromatic series, and volatile oils generally. 

 In comparing different bodies belonging to any one of these 

 groups the chemical composition or constitution is very important, 

 and if such comparisons are to be made, the solutions compared 

 must be equimolecular ; in other words, the action of a molecule 

 of one body must be compared with the action of a molecule of 

 another body. This can be done by dissolving the molecular 

 weight in grammes in, say, a litre of water (see p. 34). When 

 this is done, important facts emerge. Thus, generally speaking, 

 the compounds of a metal of high atomic weight are more 

 powerful antiseptics than those of one belonging to the same 

 series, but of a lower atomic weight. Among organic bodies, 

 ;iu r tin, substances with high molecular weight are more powerful 

 than those of low molecular weight thus butyric alcohol is more 

 powerful than ethylic alcohol and important differences among 

 the aromatic bodies are associated with their chemical constitu- 

 tion. Thus among the cresols the ortho- and para-bodies re- 

 semble each other in general chemical properties, and stand apart 

 from metacresol ; they also are similar in antiseptic action, and 

 are much stronger than the meta-body. The same may be 

 observed in other groups of ortho-, meta-, and para-bodies. 

 Again, such a proj>erty as acidity is important in the action of a 

 substance, and, generally speaking, the greater the avidity of an 

 acid to combine with an alkali, the more powerful an antiseptic 

 it is. With regard to oxidising agents and reducing agents, 

 probably the possession of such properties has been overrated as 

 increasing bactericidal potency. Thus in the case of such re- 

 ducers as sulphurous acid and formic acid, the effect is apparently 

 chiefly due to the fact that these substances are acids. Formic 

 acid is much more efficient than formate of sodium. In the case 

 of permanganate of potassium, which is usually taken as the 

 type of oxidising agents in this connection, it can be shown that 

 the greater amount of the oxidation which takes place when this 

 agent is brought into contact with bacteria occurs after the 

 organisms are killed. Such an observation is, however, not 

 conclusive as to the non-efficiency of the oxidation process, t < 

 the death of the bacteria might be due to the oxidation of a 

 \<TY small part of the bacterial protoplasm. Apart from the 

 chemical nature of antiseptic agents, the physical factors con- 



