LACTIC ACID. 679 LACY. as this activity ceases as soon as the medium becomes strongly acid, clialk 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, leadily absorbing moisture and mi.ing in all ])roportions with water and with alcohol. The ordinary phannaceutical product is iui 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 (COOH) and a secondary alcohol group (CHOH). It is a comparatively unstable substance, and when heated with dilute sul- phuric acid readil.v decomposes into formic acid and ordinary aldehyde, according to the follow- ing equation: CH,CH(OH)C0OH = HCOOH + CH^CHO Lactic acid Formic acid Aldeliyde Among the salts of lactic acid may be mentioned the lactate of calcium (C3Hj03),Ca -|- 5H,0. and the lactate of zinc (C',HA):Zn + 3H,0. which are readily soluble in hot water and almost insoluble in cold alcohol. A method of separating the dif- ferent varieties of lactic acid is based on the difterent solubilities of their zinc and calcium salts. (2) Harcolactic acid, or para-lactic acid, has the same chemical composition and constitution as ordinary lactic acid. It is found in blood, and under certain conditions in urine, as well as in various pathological lluids; it is a char- acteristic constituent of muscles, and is there- fore contained in considerable quantities in Lie- big's meat extract. Sarcolactic acid possesses considerable importiince from a physiological jioint of view. The energy of an active muscle is found to be proportional to the acidity of the muscle: and as that acidity is due to a great extent to the formation of sarcolactic acid, it is clear that the production of muscular energy- is due largely to the transformation of nitro- genous matter into sarcolactic acid. .Sarco- lactic acid may be prepared from Liebig's ex- tract of meat. It has precisely the same chemi- cal properties as ordinary lactic acid, from which it differs, however, in certain physical proper- ties; unlike ordinary lactic acid, it is optically active, and the solubility of its zinc and calcium salts is different from that of the lactates. Sar- colactic acid, as well as another variety, viz., (3) LfTvorotatory lactic acid, may be obtained from ordinary lactic acid by subjecting the strychnine salt of the latter to a process of frac- tional crystallization. The relation between the above three varieties of lactic acid is explained by the theories of modern stereo-chemistry (q.v.) . (4) Ethylene-laciic acid, or ^-hvdroxv-pro- pionic acid," CH.(OH) .CH-.COOH, often called hydracrxilic arid, is a sour, syrupy liquid readily breaking up into acrylic acid and water, accord- ing to the following equation: CH, ( OH ) .CHXOOH = CH. : CH.COOH + H;0 Hydracrylic acid Acrylic acid Hydracvvlic acid was formerly supposed to oc- cur in the animal body, but this has been shown to be incorrect. LACTIC FERMENTATION. See Febmen- T.VllO.N ; L.VCTIC Aciu. L ACTOM'ETEB, ( from Lat. lac, milk + Gk. tLirpov, nuJnjit, measure). A special form of hydrometer (q.v.) used for determining the spe- cilic gravity of milk, for the purpose of detecting adulteration with water. As usually construct- ed, the scale, which is about four inches in length, is divided into 120 equal degrees, the zero being the point to which the instrument sinks in pure water at a temperature of 60 de- grees Fahrenheit (15.50 degrees Centigrade), while the 100th degree corresponds to the spe- cific gravity 1.029, and the 120th degree to the speeilic gravity 1.0348. Experience has shown that the specific gravity of mi.xed milk from healthy cows, when taken at least twelve hours after milking, will not fall below 1.02'J. .See Milk ; Adlltlratiox. LACTUCA'RIXTM ( Xeo-Lat.. from Lat. lac- turn, lettuce, from Inc. milk). A drug consisting of the concrete juice of the Lactiica aaliva, or garden lettuce. It appears in the market in two forms. The English lactucarium is in irregular jjieces the size of a pea, while the tiernian va- riety is in pieces about an inch by a half inch in measurement. It is dark brown or light yel- lowish brown, with a faintly narcotic odor and bitter taste. It owes its efficiency to a crystal- livable bitter principle, lactucin, probably first discovered by Aubergier. It is a very feeble antispasmodic and hypnotic. It has been called 'lettuce-opium,' and in the form of syrup was once popular. LACTJ'NAB, (Lat. lacunar, panel, from la- cuna, pit. from lacus, lake). A sunken panel or coffer in a ceiling, and also in the soffits of classic cornices. Lacunars are much used in por- ticoes and similar classic structures, and are fre- quently ornamented with paters. The ceilings of many Christian churches were so decorated during the Renaissance — as, for example, the gilt ceiling of Santa Maria Maggiore in Rome. The word is synonymous with caisson, which is also given to the same decorative form when used not on horizontal ceilings, but on cuncd surfaces, such as those of the tunnel vaults and domes of Roman temples and baths, and the vaults of triumphal arches. These were usually carved in stone or marble, but were sometimes of stucco or wood, especially in post-classic times. They are seldom found except in Roman and Renaissance Imilcling-; and their modem copies. LACT, lli'se. Fraxz Mobitz. An Austrian field marshal. See La.scy, Fb.xz Mobitz. LA'CY, Hugh de (?-I186). One of the Eng- lish conquerors of Ireland. He was probably a son of Gilbert de Lacy, and before 1163 was in possession of his father's estates. In October, 1171, he went over to Ireland with Henry II., and soon was playing an important rOle. He received the grant of Meath. and was at one time also in charge of Dublin. While Governor of Ire- land, he was accused of seeking to become King of Ireland, having married in ll.Sl the daughter of Roderic. King of Connaught. But whatever his intentions were, before they could l>e realized he was murdered by a native (July 25, 1186). LACY, .ToHN ( ?-16Sl ) . An English actor and playwright. He began his London life in 1631, as apprentice to ,Tolin Ogilby. a dancing-master; held a commission in the Royalist array during
