of the system at the time, the reserves have to be drawn upon, and loss of weight is the result. Fluctuations often occur in the same individual, according to the surroundings in which he is at the time placed as regards climate, activity, and other agencies influencing the processes of oxidation. Thus, a diet that is amply sufficient for a sedentary life would not meet the requirements of an active, open-air life. Conversely, the body when called upon to undertake great muscular activity may be able to utilise a, diet that in times of less activity would burden it with waste matter and lead to disturbances of health.

Albuminoids are recognised as the chief tissue-forming foods, and they are therefore needed to supply the body waste that is continually taking place to a greater or less extent. By increasing the activity of oxidation, albuminoids produce in the body increased rapidity of tissue change. In circumstances where oxidation is especially rapid, as in vigorous persons undergoing hard muscular exertion in the open air, larger supplies of food, with a greater proportion of nitrogenised elements in the diet, are required than in those who are less actively employed, or in the same persons when leading a more sedentary life. It may, however, very well be questioned whether albuminoids are ever necessary or desirable in the amounts consumed by many persons, and assuredly whenever we are brought face to face with defective elimination of nitrogenous waste, the albuminoid constituents of the dietary should be limited.

In youth, during the period of growth and building-up of the body, when muscular and nutritive activity are greatest, larger supplies of alimeut, and especially of the tissueformers, are digested and well assimilated than in later life when the period of growth has passed, and when bodily activity is not so great.

On the other hand, old people are apt to make the mistake of adhering to a diet consisting more largely of albuminoids than the diminished wants of the system in advanced age

require. The result is a condition of discomfort or of distress induced by the inability of their organs to excrete the amount of nitrogenous waste matter that arises from the use of such a dietary.

The nitrogenous principles in foods, although primarily necessary for the maintenance and repair of the tissues of the body, are known to assist also in the production of force and heat. In the latter properties, however, they are secondary to the carbo-hydrates and fats.

Life is not sustained by a non-nitrogenous diet, but the carbo-hydrates and fats when combined with albuminoids are the great force and heat producers. They do not tend to increase tissue change, and any surplus of them left in the body may be stored up against future needs. Failure on the part of the system to assimilate and elaborate its supplies of the carbo-hydrates constitutes a grave defect in nutrition, notably exemplified in the case of diabetes.

The importance of fresh vegetables and fresh meats as bearers of extractives and salines, apart from their actual nutritive value, has been fully established, but is frequently overlooked in ordinary dietaries. If proof of this were wanting, we have it in the fact that evil consequences speedily follow the withdrawal from the dietary of the important vegetable salts. Such consequences reach their climax in attacks of scurvy and allied disorders.

Concerning the condition of the digestive organs themselves, it will suffice here to mention these four essentials of vigorous digestion, namely, a healthy condition of the mucous membrane, a due supply of normal gastric juice, sufficient nervous stimulus and good muscular tone to ensure proper rhythmic movements. Each of these is important in its own place, as separate consideration of them will show; and if one or all of these conditions be impaired or absent, difficulty of digestion will result, in a more or less pronounced form, according to the extent to which the defect exists.

As regards, in the first place, the condition of the healthy gastric mucous membrane, our knowledge has been gained mainly by direct observation. Those rare instances in which it has been possible to observe, through a fistulous opening in the stomach-wall, the actual appearance of the healthy mucous membrane when it is at rest, and also the changes that occur during the process of digestion, have taught much that is of great practical importance in relation to diet, both in health and in the different degrees of disorder and disease. The well-known opportunity of this kind, that was fully taken advantage of by Dr. Beaumont some sixty years ago, occurred in the person of a healthy young Canadian, Alexis St. Martin, who was accidentally wounded by the discharge of a gun. The shot, entering the left side and perforating the stomach, carried away part of its anterior wall. The man passed through a severe and protracted illness, but ultimately regained his health. The opening, however, never closed, and by means of it Dr. Beaumont made his valuable observations, which have since been confirmed and, in some particulars, amplified and corrected by experiments on animals.

The healthy stomach when empty is contracted, and its surface is pale; its vessels small and tortuous. When, however, food passes down the oesophagus and is received into the stomach, the pink, velvety appearance of the mucous membrane is seen to give place to a brighter, slightly darker shade; the vessels dilate and become more full of blood, and the secretion of gastric juice commences. Experiments have further shown that the same results follow upon the introduction of food through an external opening, or upon stimulation by means of a smooth body introduced from without, and gently rubbed against the inner surface of the stomach. In the latter case the effect soon passes off. If, however, the stimulus be carried to such an extent as to cause irritation, effects exactly the opposite of those described above are produced, namely,

contraction of the vessels, suppression of the gastric juice, and the secretion in its place of a quantity of mucus. The importance of this physiological fact will appear subse- · quently on many occasions.

Absorption is an important part of the process of digestion. If the stomach of a healthy animal be ligatured at the pylorus, and food be introduced by the oesophagus, it will be found that a considerable portion of the food is absorbed by the stomach. If the mucous membrane be not healthy and active the transudation goes on very slowly, or does not take place to any appreciable extent.

Now as regards the second condition, namely, a due supply of normal gastric juice. Proteids that have undergone coagulation are very insoluble, even under the action of strong acids; but they are readily acted upon by the gastric juice. It is necessary that the alkalinity of the food as swallowed should be neutralised, and not only neutralised, but converted into an acid state, in order that digestion in the stomach may proceed satisfactorily. It is a well-known fact that if the products of digestion be removed as they are formed, and if the acidity be kept up to the.normal standard, a very large amount of food will be digested by a given, and, relatively, very small, quantity of gastric juice. When the acidity of the gastric juice is neutralised its digestive action. ceases, and in such circumstances fibrin may remain in it for a long time without being digested. If, however, the gastric juice that has been neutralised be again brought up to the standard acidity, it becomes as active as it was before. When a large quantity of fibrin is placed in a small quantity of gastric juice digestion soon ceases, but if sufficient hydrochloric acid be added, digestion speedily recommences.

Given, then, a healthy mucous membrane, a sufficiency of normal gastric juice, and an absence of any abnormal nervous interference, the comparative digestibility of food is mainly determined by mechanical conditions, which pro

mote or retard the action of the gastric juice upon it. The greater the amount of surface that is presented to the action of the gastric juice, the more quickly will solution take place. Hence tough, doughy substances, that cling in masses, and firm, unbroken fibres, whether of animal or vegetable tissue, longer resist solution in the gastric juice than friable, minutely divided particles. It need hardly, therefore, be pointed out that thorough mastication of food is of the utmost importance, since by that means minute subdivision is secured, and consequently a vastly increased surface-area is presented for the action of the gastric juice. Moreover, in the case of carbo-hydrates, in addition to the mechanical effects of prolonged mastication, their digestion is begun in the mouth, by the action of the saliva converting them into dextrin,

In speaking of the appearance of the healthy gastric mucous membrane, it was implied that the stomach when empty and contracted is at rest. On the introduction of food, however, or when the stomach is stimulated in other ways, certain movements are set up. On the first entrance of food into the stomach there are but feeble indications of movement; hence it is evidently not the fact of the stomach being filled that causes the movements. If that were the cause, they would be greatest at the beginning, whereas observations show that they increase and become more marked as digestion proceeds, till they attain a rhythmic, churning action. clearly an essential part of any mere mechanical cause. fresh portions of the food of the gastric juice.

The movements, therefore, are digestion, and are not due to By these regular movements are brought under the action

In health, as has been already pointed out, a dietary is suitable or well-balanced when it is properly adapted to the wants of the individual, and contains a due proportion of nitrogenous elements, of carbo-hydrates, of fats, and of salines, with water. Clinically, however, the definition does