The Boston cooking-school cook book

exists in the juices of almost all plants, coming from the stems, branches, and fruits. Examples: gum arabic, gum tragacanth, and mucilage. Pectose exists in the fleshy pulp of unripe fruit; during the process of ripening it changes to pectin; by cooking, pectin is changed to pectosic acid, and by longer cooking to pectic acid. Pectosic acid is jelly-like when cold; pectic acid is jelly-like when hot or cold. Cellulose constitutes the cell-walls of vegetable life; in very young vegetables it is possible that it can be acted upon by the digestive ferments; in older vegetables it becomes woody and completely indigestible. FATS AND OILS Fats and oils are found in both the animal and vegetable kingdom. Fats are solid; oils are liquid; they may be converted into a liquid state by application of heat; they contain three substances,—_stearin_ (solid), _olein_ (liquid), _palmitin_ (semi-solid). Suet is an example where stearin is found in excess; lard, where olein is in excess; and butter, where palmitin is in excess. Margarin is a mixture of stearin and palmitin. The fatty acids are formed of stearin, olein, and palmitin, with glycerine as the base. Examples: stearic, palmitic, and oleic acid. Butyric acid is acid found in butter. These are not sour to the taste, but are called acids on account of their chemical composition. Among animal fats cream and butter are of first importance as foods, on account of their easy assimilation. Other examples are: the fat of meats, bone-marrow, suet (the best found around the loin and kidneys of the beef creature), lard, cottolene, coto suet, cocoanut butter, butterine, and oleomargarine. The principal animal oils are cod liver oil and oil found in the yolk of egg; principal vegetable oils are olive, cottonseed, poppy, and cocoanut oils, and oils obtained from various nuts. Oils are divided into two classes, _essential_ and _fixed_. Essential oils are volatile and soluble in alcohol. Examples: clove, rose, nutmeg, and violet. Fixed oils are non-volatile and soluble in ether, oil, or turpentine. Examples: oil of nuts, corn meal, and mustard. Fats may be heated to a high temperature,