In the remedy just mentioned the salicylic acid forms the basis; but sometimes chloride of zinc or lactic acid is added to it to make it act more quickly, and these are the adjuvants.
It is difficultly fermented by yeast, but readily by the lactic acid bacillus.
The first class include such changes as the alcoholic fermentation of sugar solutions, the acetic acid fermentation of alcohol, the lactic acid fermentation of milk sugar, and the putrefaction of animal and vegetable nitrogenous matter.
The lactic acid bacilli are given either in the form of tablets or milk soured by them, or cheese made from the sour milk.
Since Metchnikoff's introduction (see Longevity) of the use of soured milk for dietetic purposes-the lactic acid bacillus destroying pathogenic bacteria in the intestine-a great impetus has been given to the multiplication of laboratory preparations containing 'cultures of the bacillus; and in recent years much benefit to health has, in certain cases, been derived from the discovery.
Glucose also undergoes fermentation into lactic acid in the presence of the lactic acid bacillus, and into butyric acid if the action of the preceding ferment be continued, or by other bacilli.
The lactic acid bacillus, always present in unboiled milk (to which the souring of milk is due), is easily destroyed by heat; but the bacillus mesentericus, often found in it, forms spores, which are not destroyed by ordinary boiling, and germinate when the milk is kept at a moderately warm temperature, producing a brisk fermentation whereby a large volume of gas is liberated.
It may be diminished or its increase prevented by a diet from which red meat and meat extracts are excluded, by the use of the lactic acid bacillus, by the administration of laxatives and cholagogues to regulate the bowels, and by the use of iodides and nitrites.
Bacillus amylobacter usually accompanies the lactic acid organism, and decomposes lactic and other higher acids with formation of butyric acid.
Lister for isolating a pure culture of lactic acid bacterium.