This section is from the book "A Treatise On Therapeutics, And Pharmacology Or Materia Medica Vol1", by George B. Wood. Also available from Amazon: Part 1 and Part 2.
This, like the substance just treated of, is much more used for its sensible than for its remedial properties. Little, therefore, need be said of it here; but the reader will find it described, in relation to all its properties, in the U. S. Dispensatory. Cochineal is a dried insect, designated as the Coccus Cacti, because it inhabits different species of the genus Cactus and allied genera, especially the Opuntia cochinillifera, or Nopal plant of Mexico. It is from that country that cochineal is chiefly imported, though it and the plant on which it feeds are now cultivated in other countries, and especially the Canary Islands. The mass of cochineal consists of grains, which are the whole dried insect, irregularly round or oval, convex on one side, convex or flat on the other, about one-eighth of an inch in diameter, marked with transverse wrinkles, and either of a reddish-gray or blackish colour. It has a faint heavy odour, a bitter acidulous taste, and in powder a purplish carmine colour. When chewed, it stains the saliva intensely red; and it owes its chief value to a colouring principle, denominated cochinilin, which is of a brilliant purple-red, and imparts its colour to water, alcohol, and ether, all of which dissolve it. It is precipitated from its watery solution by various metallic salts, with the bases of which it forms insoluble compounds, of a rich red colour. The pigment called lake is a compound of cochinilin and alumina. Carmine is the colouring principle precipitated by the salts of tin.
In relation to its medicinal properties, cochineal may be slightly stimulant to the nervous system, and has been recommended in hooping-cough and neuralgia. In the former of these complaints, a liquid mixture containing cochineal and carbonate of potassa, was highly recommended by the late Prof. Chapman,of the University of Pennsylvania. It is more used, however, as a colouring agent than as a remedy. The dose for an infant is one-third of a grain three times a day.
The Tincture (Tinctura Cocci, Br.), which, as directed in the British Pharmacopoeia, contains the virtues of two and a half avoirdupois ounces in an Imperial pint (twenty fluidounces) of spirit, may be given in a dose of from twenty drops to a fluidrachm, but is chiefly used to give colour to liquid preparations.