Definition. - A crystalline solid composed of trichloraldehyde or chloral [CCl3.COH] (an unstable, oily, and colorless fluid), with 1 molecule of water, forming the Hydrate of Chloral, the official preparation, and the only one used in medicine. Chloral itself is prepared by the action of chlorine upon alcohol, whence the name chlor-al.

Description and Properties. - Chloral hydrate occurs as separate, rhom-boidal, colorless, transparent crystals, having an aromatic, penetrating, and slightly acrid odor, and a bitterish, caustic taste. It is slightly volatilized when exposed to the air, and is freely soluble in water, alcohol, and ether, being also soluble in chloroform, benzol, benzin, carbon disulphide, and fixed and volatile oils. It liquefies when triturated with an equal quantity of camphor, menthol, thymol, or phenol.

Dose. - 5-20 grains (0.3-1.2 Gm.) [1 Gm.-15 gr., U. S. P.].

Antagonists and Incompatibles. - Chloral is incompatible with all alkalies, and calcic hydrate converts it into formate of calcium and chloroform. Strychnine, atropine, and external heat are antagonistic.

Synergists. - All the hypnotics favor its characteristic property of producing sleep. Morphine enhances its hypnotic effects, while lessening its depressing influence upon the heart.

Physiological Action. - Externally and Locally. - Chloral is germicidal, antiseptic, anesthetic, and vesicant. It produces redness and sometimes vesication when applied to the unbroken skin, and when strong solutions are brought in contact with the derma or with wounds they may even occasion sloughing, and in healthy mucous membranes excite much pain. When introduced into the system hypodermically, chloral is apt to occasion gangrenous inflammation.

Internally. - Digestive System. - Small doses are slightly sedative to the stomach, though causing a sense of burning in the throat and exciting more or less salivation. Large doses sometimes produce nausea, vomiting, and purging. The pancreatic and biliary secretions are probably slightly increased.

Circulatory System. - Full medicinal doses may at first accelerate the pulse, which soon, however, becomes slower, weaker, and softer. Under toxic doses the heart's action may be weak, rapid, and irregular, when death ensues, the heart being arrested in diastole.

A primary effect of chloral is to lower arterial tension by its depressant action upon the heart through its nervous mechanism. It acts similarly upon the vasomotor center and upon the structures in the arteriole wall, dilating the blood-vessels.

In its depressing action on the heart chloral is more pronounced than in other non-chlorinated members of the alcohol group. It is highly probable that the presence of chlorine is an important factor in this added toxic action in the circulation.

Nervous System. - Medicinal doses sometimes occasion a preliminary stage of cerebral excitement, due probably to a temporary stimulation of the circulation and possibly transitory cortical irritation. This is soon followed - usually in from fifteen to thirty minutes - by a sound, dreamless slumber, induced by a direct depression of the cortical cells of the brain. The sleep thus produced closely resembles that of physiological slumber. It usually persists for from seven to eight hours, when the patient awakes refreshed and usually without malaise or digestive disturbance.

The action on the spinal cord is one of depression, as in alcohol. The actions on the special senses resemble those of chloroform.

Respiratory System. - In full doses chloral is a respiratory depressant, rendering the breathing slower and weaker, while under toxic doses it may cease altogether from paralysis of the respiratory center.

Absorption and Elimination. - Chloral is quite rapidly absorbed, and is supposed to circulate in the blood in its original state. It is eliminated by the lungs and skin, but chiefly by the kidneys, where it reappears as urochloralic acid, which consists of trichlorethyl alcohol combined with glycuronic acid, although when an excessive amount of the drug has been taken it may be found in the urine unchanged. It usually increases the flow of urine, and reduces Fehling's solution. The presence of chloral derivatives should, therefore, always be thought of in testing for sugar.

Metabolism. - Chloral behaves in large part as chloroform on metabolism. It leads to increased proteid destruction and lessens cellular oxidative functions. It thus shows increased phosphates, nitrates, and sulphur, and by the suboxidations leads as from alcohol, to fatty degenerations. The diminution in muscular activity retards muscle metabolism, thus less oxygen is observed and less carbon dioxide is excreted. In large doses chloral exerts a destructive influence on the blood and also in blood-vessels.

Temperature. - Chloral is a decided antipyretic even in medicinal doses, while toxic doses produce a dangerous reduction of temperature. This action is doubtless owing to a diminution of heat-production because of diminished oxidation in the cells of the body and to an increase of heat-dissipation from the dilated cutaneous vessels.

Eye. - The continued use of chloral almost invariably results in a contracted pupil, unless psychic alterations supervene, when the pupillary contraction gives place to dilatation.

Untoward Action. - There may occur great anxiety; disturbances of respiration, such as spasmodic breathing and even asphyxia, together with disturbances of vision and swelling of the conjunctivae. There may also be present edema of the epiglottis, icterus, and various cutaneous eruptions commonly designated as "chloral rash."

Poisoning. - Although one of the most powerful hypnotics known, extraordinary doses of chloral have failed to prove fatal, as many as 460 grains (30 Gm.) having been given without serious poisoning. Nevertheless, 10 grains (1.6 Gm.), an ordinary dose, has been followed by toxic effects, while 15 grains (1.0 Gm.) has produced death. In view of so uncertain a power, great care is requisite in the administration of this drug.