Mr. S. Newington has drawn attention to the powerful derivative effects of the hot mustard-bath. Two handfuls of mustard powder are tied in a cloth, and pressed in hot water till a very strong extract is obtained, which is mixed with the water of a full hot bath, and after the patient has entered this (the genitals being protected by a folded towel), a blanket is laid over the bath to prevent irritation of the eyes. After five to ten minutes' stay the patient is dried and goes to bed. A similar, but milder, application is that of a sheet wrung out of mustard infusion and covered with waterproof. The effect is to strongly excite the capillary circulation in the skin, and so to relieve internal congestion, especially of the nerve-centres, and hence it greatly disposes to sleep and quiet in conditions of mental excitement. Under packing of the trunk in towels wrung out of the hot infusion the pulse came down from 108 to GO per minute in the course of two hours (Lancet, i., 1865).1

Physiological Action (Internal)

Water is an essential constituent of the animal tissues, and their healthy growth is dependent on its sufficient supply. In passing through the system, water (1) assists the circulation of the nutrient fluids; (2) renders oxidation and other chemical changes more active; (3) by its solvent action promotes absorption, secretion, and excretion; and (4) by its evaporation from the surface gets rid of superfluous heat. The tissue-change produced by medicinal water drinking is greater in the young and delicate than in robust adults; it is promoted by increase of temperature whether of the water itself or of the atmosphere; also by bodily exercise (Parkes). The ultimate result of a judicious course of water drinking is increase of weight, and (it is said) of fat (Bartholow), but if an excessive amount be taken, the blood is rendered unduly fluid, the corpuscles become paler and less healthy, and general nutrition is impaired.

1 Schuller (of Laubbach) has studied the effect of various applications of water on the cerebral circulation of rabbits after trephining and removing the cervical sympathetic on one side. Compresses over the abdomen at 50° F. caused dilatation of vessels of the pia mater; a general bath at 50° induced the same effect in greater degree. After similar applications, but quite cold, a gradual contraction of cerebral vessels occurred in five to ten minutes, and lasted for about half an hour. Warm water, 95° to 99°, applied in the same manner caused marked contraction of the same vessels. A douche over the belly and back caused alternating changes. Injections into the rectum induced moderate dilatation. Under a cold pack, gradual and strong contraction occurred, lasting often for two hours, pulse and respiration were slowed, and reflex irritability was reduced. Ice on the head caused, after a time, moderate contraction; friction over abdomen had the same effect. We can scarcely draw definite practical conclusions from these observations, but it would seem that tepid applications over the body lead to dilatation, and quite cold or hot applications equally cause contraction of cerebral vessels. Schuller considers that extreme degrees of temperature are contra-indicated in cases of hyperaemia, congestion, and anaemia of brain, and that the main good effect of baths is exerted in depleting cerebral vessels, in giving tone to the muscular coat of arteries, and indirectly the cardiac muscle, and thus improving nutrition of nerve-centres (British Medical Journal, i., 1876).

Large draughts of cold water, especially if taken on an empty stomach or when the body is heated, act injuriously, by giving a shock through peripheral nerves to the abdominal sympathetic, and may cause nausea, faint-ness, actual syncope, and in some cases even death. Draughts of warm water, if not rejected by the stomach, act more quickly than cold upon the skin and the kidneys; they usually cause or assist vomiting, but if a pint or more be taken it will often stop vomiting by distending and paralyzing the stomach. I have also known even a moderate quantity of hot water stay vomiting when ice had failed to do so; and again, a small quantity -two or three teaspoonfuls - of quite hot water, taken at short intervals, has arrested reflex vomiting, e.g., after ovariotomy.

A certain amount of fluid taken with meals assists digestion, but too much impairs it by over-diluting the gastric juice, and hurrying on the passage of the food. Its temperature is of importance, for if taken hot, especially with a substantial meal, it is liable to distend and enfeeble the stomach, while if iced, it does harm by contracting capillaries and diminishing normal blood-supply, although, indeed, a healthy stomach will tolerate, for a time at least, these and many other injurious things. Warm liquid, such as tea, taken shortly before a substantial dinner, will commonly disorder the digestive functions sooner or later, but this is not wholly due to the fluid, but to its astringency, etc., for a warm nutritious soup at the commencement of a meal suits many persons. If they are fatigued, it supplies nourishment in a form which is readily taken up, and enables solid food to be better digested.

Taken later on in the meal, at the end, or an hour or so afterwards, fluids, cold or warm, materially assist completion of the digestive process, and the onward passage of peptones and the other contents of the stomach.

It is well known that water exerts a marked influence on the fermentative process: thus sugar, anhydrous or mixed with but little water, does not ferment at all; with moderate amounts of water the vinous, and with an excess of water the acetous fermentation takes place, and it is very probable that water exerts analogous influences on the food. Bacteria will not develop in a concentrated solution of albumen.

Therapeutical Action (External)