Externally. - Applied in weak solution (5 gr. to the ounce of water), chloral hydrate is antiseptic; concentrated solutions are irritant, causing vesication. The drug is but little used externally.

Internally. - In the mouth and stomach it is also irritant unless freely diluted, a point to he observed. It has no specially sedative effect on the stomach or bowels like opium, and therefore causes neither dyspepsia nor constipation.

2. Action On The Blood

Chloral enters the blood as such, and probably leaves it for the tissues without decomposition, although Liebreich, who introduced it into the materia medica, contends that it is broken up into chloroform and formic acid in the presence of the sodium salts of the plasma. C2HC13O + NaHO = NaCHO2 + CHC13. The blood undergoes no appreciable change.

3. Specific Action And Uses

The action of chloral upon the system so nearly resembles that of chloroform, and the chemical relations of the two substances are so close, that Licbreich's theory is at first sight extremely plausible. Chloral chiefly affects the nervous system, although one of the principal dangers connected with its use depends on its direct action on the heart. Given in moderate doses (20 to 30 gr.), hydrate of chloral, after a very brief period of excitement, quickly induces drowsiness, followed by several hours' sound sleep, natural in its characters and refreshing in its effect; as a rule, without consequent confusion, headache, or drowsiness in healthy individuals. Larger doses produce deeper and more prolonged sleep, and an appearance of narcosis, the subject being difficult to rouse even by sharp stimulation. Thus far chloral manifestly acts upon the convolutions, either directly or through the cerebral circulation, or both; and is a pure and powerful hypnotic. The larger doses, however, enable us to appreciate its action, like that of chloroform, on the lower nervous centres. The spinal centres are depressed, whence diminished reflex excitability and relaxation of the muscles. The three great medullary centres are decidedly depressed: respiration becomes slow, irregular, and shallow; the heart is weakened (but chiefly in another manner, as we shall presently find); and the vaso-motor centre is lowered in activity, so that the vessels dilate generally. The peripheral sensory nerves are not specially affected. Neither are the motor nerves, or the muscles themselves, directly depressed.

Upon these several effects of chloral depend at once its value medicinally, and the drawbacks or even dangers which occasionally attend its employment. It is the most rapid, and probably the most powerful, whilst the most pure, of all the hypnotics, opium not excepted. It is therefore extensively used to produce sleep and soothe the cerebral hemispheres, in conditions of excitement, in insomnia from over-work, distress, maniacal excitement, or despondency, and in the early stages of fevers or febrile diseases, whilst the heart is still strong. It is especially valuable in delirium tremens. In the sleeplessness which attends or is caused by peripheral pain, chloral fails, for an obvious reason; or if sleep be secured by a powerful dose, the patient wakes to suffering as before. To relieve the severe pain of neuralgia it is totally unfitted.

Chloral has also been given in the delirium of the more advanced stages of fevers; to relieve the distress, dyspnoea, and insomnia of cardiac and renal disease; and in the cough, spasm, and breathlessness attending phthisis, bronchitis. and other respiratory affections. The dangers of the drug in these conditions have been shown by the fatal results which have followed its employment; and the cause of them is obvious. Besides its depressing effect on the medulla, chloxal in full doses acts as an intrinsic cardiac poison, slowing and enfeebling the heart by diminishing the irritability of its ganglia, and finally arresting it in ventricular diastole. At the same time the blood pressure falls by peripheral paralysis of the vessel walls, as well as from the interference with the vaso-motor centre, the heart, and the respiration; so that altogether the circulation tends to become arrested. Thus the relief to be obtained from chloral in the delirium of fever where the heart is threatening to fail, and in organic disease of the heart, lungs, or kidneys, is but temporary, and is purchased at serious cost; for this purpose the drug is not to be recommended.

The action of chloral in reducing the excitability of the grey matter of the cord, and higher motor ganglia, has suggested its use in tetanus, strychnia poisoning, puerperal convulsions, hydrophobia, sea-sickness, and whooping-cough. It has also been given in some cases of chorea, but here really as a hypnotic.

The exact effect of chloral on metabolism is unknown. It reduces temperature, chiefly by increased loss of heat from the dilated peripheral vessels, but also by diminishing the production in the weakened muscles, etc. It must not, however, be given as an antipyretic in high fever, unless at the commencement, in strong subjects, on account of its depressant action on the heart. It has been highly recommended in cholera.

4. Remote Local Action

Chloral is excreted by the kidneys partly unchanged, but chiefly as urochloralic acid producing slight diuresis. Probably part escapes by the skin also, as a variety of eruptions may attend its prolonged use.

5. Advantages And Disadvantages Of Chloral; Cautions; Contra-Indications

It will be well to state here succinctly the advantages and disadvantages of chloral as compared with morphia (opium). Chloral has the following advantages: It acts quickly as a hypnotic - even more quickly than morphia subcutaneously, and more certainly even when morphia has failed. After-effects, such as headache, depression, and sickness are less common from chloral. It does not derange the stomach, if freely diluted; nor cause constipation, even when given for a long time. It may be more safely given, in proper doses, to children.

On the other hand, chloral has these disadvantages: It does not relieve pain, and is thus greatly inferior to opium in most cases as a hypnotic, and useless as an anodyne. It does not, like opium, prevent or relieve distress, reflex dyspnoea, and cough due to heart and lung disease. Chloral causes excitement instead of quiet, in many cases of mania, hysteria, and confirmed alcoholism.

Chloral must be given in relatively small doses to children and delicate persons; and very rarely, as we have seen, to the subjects of organic disease of the heart, lungs, and kidneys, or patients suffering from gout. If it excite instead of soothing the insane or the confirmed drunkard, it should not he persevered with; nor if it increases instead of relieving sleeplessness in certain individuals, as it does occasionally, apparently from idiosyncrasy. Lastly, chloral must he prescribed with great hesitation to persons who suffer from constitutional debility of the nervous system, expressing itself in hysteria, despondency, excitability, and innumerable other forms. Such subjects very readily acquire the "chloral habit," that is, they consume on their own account regular and ever increasing quantities of chloral, until the nervous system and general nutrition fail, the mind is demoralised, and the victims ultimately perish like the drunkard and opium eater.