As the human body consists of close upon 70 per cent, of water, it is manifest that in one way or another its ingestion demands our careful attention. Where too little fluid is supplied, the blood maintains a higher specific gravity and the poisonous waste products of tissue or cell change are only cast off very imperfectly. In addition to being incorporated with the tissues and forming the chief ingredient of all the fluids of the body - thus enabling them to maintain their proper degree of dilution - water plays an important part in the economy by moistening the mucous and serous membranes, and thus reducing friction to a minimum. Through the fluid media of the blood and lymph it distributes the body heat, and by evaporation it regulates the temperature.

In whatever manner, therefore, it can be introduced, its supply is of prime importance. However he may sustain the deprivation of food, man can only survive for a few days without water, and even in a few hours is seriously indisposed by its restriction. As he excretes some two and a half litres (four and a half pints) per day, it is requisite that he should partake of this quantity either in association with his food and food accessories or else in the shape of pure water. Close upon a litre (one and a half pints) are usually included in his daily diet, so that leaves more than a litre and a half (about three pints) for liquid consumption. Yet few people can be persuaded to indulge in such a large quantity, and even then it is chiefly in the shape of tea, coffee, cocoa, or even alcohol, despite the well-known solvent properties of pure water. Doubtless a large number of obscure aches and pains and imperfect tissue-functioning are due to this abstention from water.

When taken to excess, especially at meal-times, it is prone to set up symptoms of indigestion, loss of appetite, sensations of "fullness," flatulence, etc. This is because the stomach can only absorb a minute proportion of its liquid contents, by far the greater part being expelled into the duodenum prior to the expulsion of its solid contents. It is remarkable, however, that this lack of capacity for absorption is not shared by other fluids, such as alcohol, the purins of meat-extracts, the essential principles of tea and coffee, all of which are rapidly taken up by the gastric mucous membrane. Hence the rapid restorative or stimulating properties of these substances, and the quick temporary relief which follows their use in cases suited for their administration.

The bowel in a state of health is quite capable of dealing with two litres (three or four pints) of water daily, in addition to the ordinary solid food.

The physical condition of water is not a matter of indifference to the system, as its effects vary according to its temperature. Cold water stimulates the flow of gastric juice, and hence is contra-indicated in hyperchlorhydria. It is less rapidly expelled from the stomach than hot water, a pint being ejected in three-quarters of an hour. It is also said to act more as a diuretic than hot water, more of which is retained in the alimentary canal. I should think, however, this question is largely one of idiosyncrasy.

All of the most intimate metabolic processes would be impossible without the presence of water. These are chiefly of the nature of hydrolysis or hydrolytic decomposition, sometimes effected by hydrolytic ferments, or they may consist in dehydration, or again of a mere loss of the water of crystallisation.

The quantity ingested varies according to the social position, habits, and habitation of the individual; but besides the amount consumed by drinking, we must take into account the "oxidation water" resulting from the combustion of hydrogen in the food. This will, of course, depend on the metabolic activity, but it is calculated that every hundred calories of food, whether fat, protein, or carbohydrates, yields about 10 grams of water. The potential energy of a mixed diet should be distributed as to one-sixth of the total amount from protein, one-third from fat, and one-half from carbohydrate, so that about 300 grams of oxidation water would be derived from 2,500 calories of food.