Action on the Circulation. - It diminishes the blood-pressure in two ways - first by weakening and finally paralysing the vasomotor centre, and thus dilating the vessels; and secondly by weakening the heart. The pulse may at first be quickened, possibly, in consequence of the lessened blood-pressure, but it afterwards becomes slow. The slowing of the pulse is not due to any action of the drug upon the vagus, for it occurs after section of the vagi, or after the previous administration of nicotine, atropine, or curare. The weakening and final stoppage of the heart appears to be due to paralysis of the cardiac ganglia, as the heart still continues to contract when its muscular substance is irritated directly.

Action on Muscles and Motor Nerves. - The muscles and motor nerves are not paralysed by chloral. The paralysis and loss of sensibility are of spinal origin.

Action on the Spinal Cord. - Chloral first increases and then diminishes the excitability of the spinal cord, and finally abolishes it altogether. It probably acts first upon the grey matter, as impressions which are usually painful are not felt at a time when tactile impressions still produce reflex.

Action on the Brain. - At first it may cause a little excitement of the brain, followed by sleep, and then by coma. These actions are probably due partly to the influence of the drug on the circulation, and partly to its direct action on the cerebral tissue itself. In the first stage of excitement the circulation in the brain is somewhat increased, but as sleep comes on the vessels contract and the brain becomes anaemic.

The pupil is almost invariably contracted; the temperature; as has already been mentioned, falls steadily and rapidly, and this fall appears to be due partly, though not entirely, to lessened production of heat, for it still occurs, though to a less extent, when the animal is wrapped up in cotton-wool, or is put in a warm place.

The Treatment of Chloral-Poisoning. - In conjunction with Professor Stricker, I found that animals which had received a dose of chloral which would certainly kill them if they were left exposed, would recover from the effects of such a dose if they were wrapped up in cotton-wool. If the dose be still further increased, so as to kill the animal even when carefully so wrapped up, it may still be kept alive by being put in a warm place, so that its temperature is kept up artificially. If, however, the dose be still further increased, the animal will die, notwithstanding these precautions. The treatment of cases of poisoning in man is the same as in animals, viz. to keep up the temperature of the patient by putting him in a warm room, covering him with blankets, applying hot bottles, and giving stimulants, coffee, etc.

Chronic Chloralism. - Despite its nauseous taste, chloral sometimes excites a craving, just like morphine, in those who have begun its use to allay nervous excitement, or to procure sleep. Taken habitually in this manner, it is apt to excite gastrointestinal disturbance, and to produce skin-eruptions (chiefly erythematous), which sometimes occur only on taking alcohol also, to lower the nutrition, and to cause pains, nervous irritability and depression, which may lead to disturbance of the mental equilibrium. After a time, the dose has to be increased to produce the desired effect, but tolerance is not so readily established as in the taking of opium or morphine, so that patients have died from a slight increase of the dose they have been accustomed to take.

Uses. - If equal parts of chloral and powdered camphor are rubbed together, they dissolve, and form a syrup. This is useful in neuralgia, when painted over or gently rubbed into the painful part. In the proportion of chloral 1 part, camphor 1 part, and simple ointment 8, it is a useful remedy in the itching of skin-diseases.

The chief use of chloral is to produce sleep. It is useful as a hypnotic in the sleeplessness due to overwork or worry, and the wakefulness depending on constitutional peculiarity, old age, or disease, such as fever, delirium tremens, insanity, and puerperal mania. In the latter stage of Bright's disease, where there is great sleeplessness accompanied by high blood-tension, chloral is very useful. The sleep which it causes is generally quiet and refreshing, and as a rule it is not followed next day by sickness, headache, and depression, like the sleep caused by opium. Usually, also, the sleep is not too deep to prevent the patient being readily awakened for the purpose of taking food.

Chloral may be used to lessen reflex excitability and diminish convulsions, as well as to produce sleep. For this purpose it is given in puerperal convulsions, in the convulsions of children, and in chorea and tetanus. In these two latter diseases it must be given in large doses. It alleviates the dyspnoea in spasmodic asthma, and the asthmatic attacks which occur in persons labouring under chronic bronchitis with emphysema. In cases of this sort, however, it is well to give it with care, for Ringer states that in them it often produces increased lividity and muttering delirium, lasting for several days.

The action of chloral as an anaesthetic or analgesic is much slighter than that of chloroform, but nevertheless it sometimes relieves pain, and for this purpose it has been used in gastralgia, intestinal and renal colic, neuralgia, and chronic rheumatism. It has been recommended by Dr. Playfair in doses of 15 grains, repeated if necessary in twenty minutes, before the os uteri has become completely dilated, to lessen pain in labour.

Chloral is an antidote to strychnine, physostigma, and picro-toxine. Liebreich states that strychnine is an antidote to chloral; and while some observers have confirmed his statement, others have denied it, so that strychnine has certainly not the same power of antagonising the action of chloral as chloral has of antagonising strychnine.

Chloral is a useful remedy in sea-sickness, and in the incontinence of urine in children.