Active Ingredients of the seeds vary accordingly as it is raw or roasted. In the raw seed, Caffeine, C8H10N4O2, is probably the only important ingredient; it crystallizes in pure white silky needles, which can be sublimed by a heat of about 350°; its vapor has no smell; it has a neutral reaction, and a weak, bitter taste; it is moderately soluble in water, in alcohol, and in ether. It combines with the stronger acids to form acidly reacting salts. It dissolves, colorless, in concentrated sulphuric and nitric acids; but, if the solution with the latter be evaporated, there is a reddish-yellow residue, which gives, with ammonia, a brilliant purple color.

In the raw seed, caffeine exists as a tannate. In the process of roasting, as was first shown by M. Personne,1 a portion of this tannate of caffeine becomes transformed into the alkaloid methylamine, a substance which, in the form of the acetate, has been proved by M. Behier 2 to possess stimulant qualities.

The volatile and aromatic ingredients of coffee are developed in the roasting; it is not accurately known either what they are, nor how far they influence the physiological action of coffee. It is possible that the whole of the undoubted increase in physiological power which the roasting confers upon the seed is due to the change of part of the caffeine into methylamine. M. Aubert has recently remarked that coffee-extractive free from caffeine is far from being inert.

One more active ingredient must be mentioned, namely, the coffee-tannin, or caffeic acid, which possesses somewhat astringent properties.

Physiological Action. - The infusion of coffee is celebrated for its stimulating and refreshing effects; but there is a certain number of persons who know it only as a more or less powerful poison, and it is probable that even less susceptible individuals would suffer from similar symptoms if they took it in very large doses. Coffee undoubtedly exalts the general reflex excitability: one of the consequences of this is its effect in banishing sleep; another is the production of an irritable state of the heart, in which the slightest excitement is sufficient to bring on violent palpitations.

1 Practitioner, October, 1868.

2 Ibid.

(The physiological effects of unburnt coffee differ decidedly from those produced by the roasted bean. For many years we have used a wine or a tincture made from green coffee for its diuretic and anti-lithic effects, which are quite marked, and find it specially useful as an eliminating agent in gouty conditions of the system, to be used during the intervals between the acute manifestations of the disease. Gubler has quite recently ascertained that caffeine is an efficient diuretic)

The action of caffeine has been very sedulously investigated by many observers; its action on the nervous system is specially illustrated by the recent researches of Aubert, already referred to. According to the latter author, caffeine, when injected in sufficient quantities into rabbits, rats, cats, and dogs, always exalts reflex excitability and produces tetanus. The latter originates in the spinal cord, the nerve-trunks remaining intact. It also causes a rigidity of the extremities, which Aubert thinks is dependent upon a direct action on the muscular tissues. The poisonous action can be overcome by the use of artificial respiration. In frogs, caffeine has but little action on the heart. In rabbits it remarkably quickens the pulse, but there are periodic intermissions in which the heart appears to be distended. In dogs the frequency of the pulsations increases, while the blood-pressure is invariably lessened; the former effect Aubert thinks due to action on the excitory apparatus of the heart, the latter to paralysis of the cardiac nerves arising from the cardiac ganglia. Upon man he did not find caffeine act very powerfully; a dose of 7.8 grains produced only confusion in the head, tremor of the hands, and quickening of the pulse. Other writers, however, have observed much more formidable symptoms, and there is little reason to doubt that, in sufficient quantity, caffeine would prove as directly poisonous to man as to animals.

Therapeutic Action. - Coffee in strong decoction is very well known as an antidote to various conditions of nervous depression.

Opium-poisoning affords perhaps the most familiar field for the reviving powers of coffee; it is a common and successful practice to ply the patient with repeated small cups of the strongest black coffee, very hot. In this way the increasing torpor of the nervous centres is arrested, and the patient's attention is kept sufficiently roused to enable him to co-operate with the physician in those unremitting muscular exercises which the latter urges him to keep up. The great object is no doubt to maintain the activity of respiration and of the eliminative processes during a certain period, after which safety will have been reached. The coffee effects this in a twofold manner: partly by direct stimulation of the brain centres, and partly by the general augmentation of reflex excitability. In this action of recovering patients from opium-stupor, it does not appear that caffeine can replace coffee. It was proposed by Dr. Campbell, of America, for this purpose, but it did not succeed in his hands; and in a subsequent case, recorded by Dr. Anstie, it had only a temporary influence.1 Either the methylamine or the aromatic principle of roasted coffee must exert some powerful influence of a stimulating kind.

In various adynamic Fevers coffee has often been used with much success; and there are some physicians who almost always employ it instead of alcohol for this purpose. Here perhaps the whole effect is not due to its mere action on the nervous system; for it has been stated by some observers that coffee has the power to diminish the febrile waste of nitrogenous tissues, as displayed in the large discharge of urea.1

1 Medical Times and Gazette, 1862.