Stimulants.—­Tea and coffee contain an alkaloid theine, besides volatile oils, tannin, &c.  Cocoa contains the milder alkaloid, theobromine.  They stimulate the heart and nervous systems; tea and coffee have also a diuretic effect.  Formerly they were erroneously thought to lessen tissue waste.  These alkaloids, being purins, are open to the general objections named elsewhere.  Stimulants do not impart energy or force of any kind, but only call forth reserve strength by exciting the heart, nervous system, &c., to increased activity.  This is followed by a depression which is as great, generally greater, than the previous stimulation.  Except, perhaps, as an occasional medicine, stimulants, should be avoided.  Analysis of cocoa shows a good proportion of proteids and a very large quantity of fat.  The claim that it is a valuable and nutritious food would only be true if it could be eaten in such quantities as are other foods (bread, fruits, &c.).  Were this attempted, poisoning would result from the large quantity of alkaloid.  The food value of half a spoonful or thereabouts of cocoa is insignificant.  Certain much advertised cocoa mixtures are ridiculous in their pretentions, unscientific in preparation, and often injurious.

Cereals.—­The most valuable is wheat, from its proteid being chiefly in the form known as gluten.  From its tenacity, gluten enables a much better loaf to be produced from wheat than from any other cereal.  The outer part of the grain is the richest in mineral matter and proteid.  Wheatmeal bread shows a considerably higher proteid value than white.  A large proportion of the proteid in the outer coats of the wheat berry is, however, not digested, and in some experiments the waste has been enough to quite nullify its seeming advantage over white bread.  Coarsely ground, sharp branny particles in bread irritate the intestines, and cause excessive waste of nutriment; but finely ground wheatmeal is free from this objection, and is beneficial in preventing constipation.  The comparative value of white and brown bread has been much discussed; it depends both on the quality of the bread and the condition of the digestive organs.  Experiments on the digestion of bread and other things, have often been made on persons unaccustomed to such foods, or the foods have been given in excessive quantity.  To those accustomed to it good wheatmeal bread is much pleasanter, more satisfying, and better flavoured than white; indeed, the latter is described as insipid.  Most bakers’ bread is of unsatisfactory quality.  Flour and bread contain very little fat, the absence of which is considered a defect.  This is remedied by the addition of butter, fat or oil, or by nuts, &c., which are rich in oil.  These may be mixed with the flour prior to cooking, or used afterwards.

Oats contain a substance called avenin, apparently an alkaloid, which has an irritating action; the quantity is variable.  It is to this that the so-called heating effect of oatmeal on some persons is due.