If to a mixture of yeast, or any nitrogenous substance, and water, sugar, and then chalk, be added, and finally a very small quantity of this greyish substance, taken from a portion of a liquid undergoing active lactic fermentation, lactic acid fermentation is almost immediately set up, the chalk disappears owing to the formation of calcic lactate, and the greyish substance is copiously deposited. When placed under the microscope this ferment is seen to be composed of “little globules, or very short articulations, either isolated or in threads, constituting irregular flocculent particles, much smaller than those of beer yeast, and exhibiting a rapid gyratory motion.” If these little particles be washed thoroughly in pure water, and then placed in a solution of sugar, lactic acidification immediately commences in the saccharine liquid, and goes on steadily until stopped by the excess of free acid.
LAC′TIDE. See Lactic acid.
LAC′TIN. See Sugar of Milk.
LAC′TOMETER. Syn. Galactometer. An instrument for ascertaining the quality of milk. Milk may be roughly tested by placing it in a long graduated tube sold for the purpose, and allowing it to remain until all the cream has separated and measured, then decanting off the clear whey, and taking its specific gravity; the result of the two operations, when compared with the known quantity of cream and the density of the whey of an average sample of milk, gives the value of the sample tested. See Milk.
A little instrument called a ‘milk-tester’ is sold in London at a low price. It is essentially a hydrometer which sinks to a given mark on the stem in pure water, and floats at another mark at the opposite end of the scale in pure milk. The intermediate space indicates the quantity of water (if any) employed to adulterate the article. As the sp. gr. of pure milk varies, the indications of the ‘tester’ cannot be depended on.
LAC′TOSE. See Sugar of Milk.
LAC′TUCA. (B. P.) Syn. Lettuce. The leaves and flowering tops of the wild indigenous plant Lactuca virosa. They are sedative, narcotic, and powerfully diuretic; also mildly laxative and diaphoretic. Given in dropsy and visceral obstructions. See Lettuce, Extract of.
LACTUCA′′RIUM. Syn. Lettuce opium. Thridace; Lactucarium (Ph. E. & D.). The inspissated milky juice of the Lactuca sativa (common garden lettuce), or the Lactuca virosa (strong-scented wild lettuce), obtained, by incision, from the flowering stems, and dried in the air. The latter species yields by far the greatest quantity. M. Arnaud, of Nancy, adopts the following method of procuring this substance, which appears to be the most productive and simple of any yet published:—Before the development of the lateral branches, the stems of twelve plants are cut, one after another, a little below the commencement of these branches; returning to the first one, a milky exudation is found on the cut portion, and on that which remains fixed in the earth; this milky exudation is adroitly collected with the end of the finger (or with a bone knife), which is afterwards scraped on the edge of a small glass; the same operation is performed on twelve other heads, and so on; on the third day it is repeated on every portion of the plant remaining in the ground, a thin slice being first cut off the top; this is done every day until the root is reached. As soon as the lactucarium is collected it coagulates; the harvest of each day is divided into small pieces, which are placed on plates, very near each other, but without touching, and allowed to dry for two days, after which they are set aside in a bottle. In this way 15 or 20 times the ordinary product is obtained.
Prop., &c. Lactucarium is anodyne, hypnotic, antispasmodic, and sedative, allaying pain and diminishing the force of the circulation. It has been recommended in cases in which opium is inadmissible, and has been administered with advantage in chronic rheumatism, colic, diarrhœa, asthma, and troublesome cough of phthisis, the irritability and watchfulness in febrile disorders, &c.—Dose, 2 to 5 gr.; made into pills, lozenges, or tincture.
LACTU′CIN. Syn. Lactucinum, L. This is the active principle of lactucarium, and is found in the juice of several species of lettuce.