Alcohol at a strength of about 10 per cent. and upwards acts as a preservative of many organic substances. and is often added to medicinal preparations, extracts, wines, etc., to prevent putrefactive deterioration. In the absence of better antiseptic remedies it may serve as a useful application to wounds if used somewhat freely and of not too low a strength – say 50 to 80 per cent.
In many spirituous liniments the alcohol, apart from any purpose which it may serve as solvent or antiseptic, has a mild effect as a counter-irritant, since when well rubbed into the skin it dilates the blood-vessels. When, on the other hand, it is used as a lotion merely to bathe the surface of the skin, and allowed to evaporate, it produces a cooling effect and diminishes the amount of sweat excreted. Hence its use, in the form of Eau de Cologne, Florida water, lavender water, and so on, to soothe certain forms of headache.
Strong alcohol absorbs water from animal and vegetable tissues. thereby hardening them; it is therefore employed for dehydrating histological specimens preparatory to cutting sections therefrom for microscopical examination.
According to Russell and Buddin,1 neither methyl alcohol nor ethyl alcohol is nearly so effective in sterilising soil as might be supposed, the minimum effective doses being, respectively, 32 and 46 per cent. of the weight of the soil.
Beyer2 has found that alcohol of 70 per cent. strength by weight (769 by volume) is more effective as a bactericide than alcohol of any other strength. At above 80 per cent. (by weight) it is almost useless as a disinfectant, since strong alcohol preserves bacteria by drying them. Even absolute alcohol does not kill dry bacteria.
The addition of chloroform, ether, benzene, acetone, glycerine, carbon disulphide, or petroleum ether, does not increase the bactericidal power of alcohol; but Eau de Cologne – a spirituous solution of perfume oils – has a more powerful disinfectant action than plain alcohol.
Comstock, however, has investigated the germicidal action of alcohol on the organisms Bacillus subtilis, B. anthracis, B. coli communis, and Streptococcus pyogenes aureus, and concludes that it has but little value as an antiseptic against these micro-organisms, whether the strength is 95 per cent. or 70 per cent.