LACTIC (f•om Lat. lac, milk) ACID. A name applied to several organic acids having the composition corresponding to the formula (1) Ordinary laclic acid, or ethylidene lactic acid, CILCH (OH)COOH. is a characteristic constituent of sour milk. in which it was discov ered by Scheele in 1780. It is formed, in gen eral, whenever sugar or starch undergoes lactic fermentation in the presence of decaying nitro genous matter, or when sugar is heated with alkalies. It is found in the stomach and intes tines, as well as in the brain and in muscles. It may be readily prepared by keeping a mix ture of cane-sugar solution and sour milk to which a little decaying cheese and some chalk have been added, for two weeks at a tempera ture of about 40° C. (104° F.). The transforma tion is caused by the activity of the so-called lactic ferment (Bacillus ((Icarus Ilueppc), and as this activity ceases as soon as the medium becomes strongly acid, chalk must be added to neutralize the lactic acid produced. Further,
the process must not be kept up too long, as an other fermentation may set in, by which the lactic acid would be transformed into butyric acid. When obtained in the pure state, lactic acid forms a transparent, colorless, syrupy liquid, icadily absorbing moisture and mixing in all proportions with water and with alcohol. The ordinary pharmaceutical product is an aqueous solution containing about 75 per cent. of lactic acid. It has been used in diluted form, to dis solve the membrane in diphtheria, and as an ingredient of stomachic mixtures. Chemically lactic acid is at once an acid and a secondary alcohol, its molecule containing both a car boxyl group (C0011) and a secondary alcohol group (CIIOH). It is a comparatively unstable substance• and when heated with dilute sul phuric acid readily decomposes into formic acid and ordinary aldehyde, according to the follow ing equation: