Those of interest to us are lecithin and cholesterol. Lecithin is found in certain animal tissues, especially the central nervous system and the yolk of egg. Of the fatty substances of the latter, it constitutes about 70 per cent. It is a compound of glycerin and choline with stearic, palmitic, and phosphoric acids, and is chemically a complex glycerophosphate. It can be saponified by alkalies. (See Phosphorus.)

Cholesterol, a monatomic alcohol, C26H43OH, is a crystalline body found in all forms of protoplasm, but especially in brain tissue. It also occurs in abundance in the yolk of egg, in milk, cream, and butter, and in the bile. Gall-stones are frequently the result of its precipitation in the bile-ducts or gall-bladder. It has been suggested in anemia, especially pernicious anemia, in doses of 15 grains (1 gm.) three times a day; but it is best given in the form of milk and eggs. Quite probably it plays no role in therapeutics.

Lanolin (adeps lanae hydrosus), the purified fat of the wool of sheep, mixed with 30 per cent. of water, is made up of compounds of various fatty acids with isocholesterin. It is thus not a glyceryl fat, but a cholesterin fat, and is often classed with the waxes. It is yellowish white, of soft, sticky consistence, and, unlike the glyceryl fats, cannot be saponified by boiling with an aqueous solution of potash. Its greatest interest for us consists in its power to absorb more than its own weight of water, which makes it of use as an ointment base for substances in aqueous solution. It is a secretion of the sebaceous type, not absorbable by the sheep's skin. As to its absorbability by the human skin there are conflicting reports, but most observers claim ready absorption. Patschkowski applied an ointment of lanolin and potassium iodide and obtained iodine in the urine in half an hour. Bloor states that it is not absorbed when administered by mouth.

The waxes are esters of the fatty acids with hydrocarbon radicles higher in the series than glyceryl. They are of firmer consistence than the fats, have a higher melting-point, and cannot be saponified by boiling with an aqueous solution of potash.

Beeswax is from the honey-bee, and is known in pharmacy as yellow wax (cera flava). When bleached it is called white wax (cera alba). It is chiefly myricyl palmitate, C30H61.C16H31O2.

Spermaceti (cetaceum) is obtained from the head of the sperm-whale, a single whale yielding many barrels. It consists chiefly of cetyl palmitate, C16H33C16H31O2. The best "cold-creams" contain spermaceti and white wax; the poor ones are made of tallow.

The ointments or salves in common use are prepared mostly from lard, suet, lanolin, white wax, yellow wax, spermaceti, and petrolatum (a mineral product).

The mineral oils do not belong among the constituents of organic drugs, but for convenience may be mentioned with the other oils. They are petroleum products, are mixtures of hydrocarbons, and are not subject to rancidity. The official petroleum products are:

Petroleum benzin (benzinum purificatum - see Part II). (Kerosene oil is a limpid petroleum product from which, for safety, the more volatile hydrocarbons are removed by distillation. It is not official.)

Liquid petrolatum (liquid paraffin) is a much heavier and more oily liquid than kerosene. Trade names for some of its slight modifications are "liquid albolene" and "liquid vaseline." It has a specific gravity of 0.828 to 0.905 at 250 C. That having a viscosity of 3.1 or over is known as "heavy liquid petrolatum," and that with a viscosity of 3 or less is "light liquid petrolatum."

Petrolatum (petrolatum) is practically what we know as vaseline. The Pharmacopoeia specifies "without odor or taste."

White petrolatum (petrolatum album), a decolorized product, has been marketed under the trade names of "solid albolene" and "white vaseline."

Paraffin (paraffinum) is a white, waxy solid, the purified residue left after the liquid portion of the crude petroleum has been removed.

Petrolatum and white petrolatum are of ointment consistence, and have the advantage in ointments of not becoming rancid. But their value in ointments is limited, as they are not absorbed through the skin and do not readily penetrate animal and vegetable parasites. In intestinal or pancreatic fistulae, vaseline and paraffin, being non-saponifiable, have been found efficient in protecting the skin from erosion; while the salves containing lard or other animal or vegetable fats become saponified by the alkaline secretions and are useless or harmful. Rovsing recommends vaseline as an injection into the joint in dry arthritis; and Wilkie, the liquid vaseline to prevent adhesions in abdominal surgery. The writer has employed liquid petrolatum in the dry joints of rheumatoid arthritis with temporary benefit. Liquid petrolatum is used as the vehicle in oily sprays for nose and throat, as the agent of suspension of the insoluble salts of mercury for hypodermatic use, as a softening enema for hard feces, and by mouth, as a mild laxative; dose, 1 ounce (30 c.c.) two or three times a day. (See Cathartics, Part II.) Kerosene and liquid petrolatum, taken internally, are completely unab-sorbed, and serve merely to increase the bulk of the intestinal contents and to soften the feces. They retard the emptying of the stomach. Paraffin with added resorcin, eucalyptol, or other antiseptics is used to make a wax dressing for burns.