This section is from the book "Materia Medica And Therapeutics - Vegetable Kingdom", by Charles D. F. Phillips. Also available from Amazon: Materia Medica And Therapeutics: Vegetable Kingdom.
Active Ingredients. - The Oleum Theobromae is a concrete oil obtained from the ground seeds by expression and heat, and appears to be composed chiefly of stearine with a little oleine. The consistency is that of tallow; in color it is yellowish; the fracture is clean, presenting no indications of an admixture of foreign matter; exposure to the air does not render it rancid; in water it is insoluble, but in alcohol, ether, and oil of turpentine it dissolves; it melts at a temperature of 122°. To these qualities are added a bland and agreeable flavor, and an odor resembling that of chocolate. Good shelled cocoa-beans contain about 52 per cent. of this oil.
The oil or butter is the only ingredient of cacao which is officinally recognized, but the seeds also contain a substance of very different character, which must be taken into account in estimating the effects of cocoa and chocolate used as a beverage, viz., Theobromine. This alkaloid, C7H8N4O2, forms microscopic white rhombic needles with a strong, bitter taste, which develops but slowly on the tongue; it is tolerably soluble in water, less so in alcohol, very little soluble in ether. Hot solutions become opaline as they cool. The percentage of theobromine in cacao seeds has been very differently stated, but apparently the quantity must be very small, since, as we shall see, it is a powerful poison.
Physiological Action. - The oil of cacao can only be considered as a bland oleaginous food; it serves, however, a mechanical purpose as a good vehicle for the making up of soluble pessaries, suppositories, etc.
Theobromine is a very powerful poison, the action of which has been especially investigated by Mitscherlich. In rabbits the early symptoms were grinding of the teeth, slowing of respiration (often as much as to the third or the fourth of the normal rate), and increased rapidity of pulse, with weakened heart-pulsation. The further symptoms varied according to the rapidity of absorption; when this was great, there Were convulsions of spinal origin; but when absorption was slow, there was gradual loss of voluntary power. The secretions, appetite, throat, etc, did not seem affected. Retching and vomiting were occasional symptoms. In frogs there was great distention of the lungs and of the bladder.
Death occurred with phenomena of vagus and spinal cord paralysis; the spinal convulsions in cases of rapid absorption hastened the end. Dissection showed appearances corresponding to the symptoms: when death occurred very rapidly, there was long-continued irritability of the voluntary muscles, and persistence of peristaltic movements; when the poisoning had been slower, the heart and muscles were found quite inirritable, the ventricles were contracted, the auricles, great venous trunks, and small vessels, in all parts of the body (especially in the mucous and serous membranes, the brain, liver, and kidneys), were very hyperaemic; there were extravasations of blood almost always in the lungs, and frequently in the mucous membranes and under the peritoneal covering of the bladder; the blood was dark-red, and speedily became oxidized on exposure to air. Mitscherlich concluded that theobromine was a poison of the same general kind as caffeine, but fatal in much smaller doses. It can be absorbed either from the stomach or from the subcutaneous tissues.1
Therapeutic Action. - The present employment of the oleum theobromae is in the preparation of suppositories which have for their ingredients tannic acid, mercury, morphia, or lead. Theobromine has not yet been applied to any therapeutic purpose, but it could probably be used with advantage in nervous affections of the same kind as those which are relieved by caffeine, only in smaller doses.
In regard to the dietetic use of cocoa and chocolate as substitutes for tea and coffee, it may be said that the chief advantage of the two former is the predominance of nutrient over stimulating ingredients in their composition. Cocoa and chocolate are really foods, with only so small a proportion of alkaloidal stimulant as probably just serves to render digestion more active.