Diet in Infancy.— No food has as yet been found so suitable for the young of all animals as their mother’s milk. And this has not been from want of seeking. Dr Brouzet (four (’Education médicinale des Enfants, i. ρ. 165) has such a bad opinion of human mothers, that he expresses a wish for the state to interfere and prevent them from suckling their children, lest they should communicate immorality and disease! A still more determined pessimist was the famous chemist Van Helmont, who thought life had been reduced to its present shortness by our inborn propensities, and proposed to substitute bread boiled in beer and honey for milk, which latter he calls “brute’s food.” Baron Liebig has followed the lead with a “Food for infants,” ip the prescription for which half ounces and quarter grains figure freely, and which has to be prepared on a slow fire, and after a few minutes boiled well. And after all not nearly such a close imitation of human milk is made as by the addition to fresh cow’s milk of half its bulk of soft water, in each pint of which has been mixed a heaped up teaspoontul of powdered “sugar of milk” and a pinch of phosphate of lime. Indeed, in default of these cheap chemicals, the milk and water alone, when fresh and pure, are safer than an artificial compound which requires cooking. And experience shows that the best mode of administering food to the young is also that which is most widely adopted throughout warm-blooded nature, namely, in a fresh, tepid, liquid state, frequently, and in small quantities at a time.

Empirical observation is fully supported in these deductions by physiological aud chemical science. Milk contains of— [table]

These are at once the constituents and the proportions of the constituents of food suited to a weakly rapidly-growing animal. The large quantity of water makes it pass easily through the soft absorbent w alls of the digestive canal, and the complete suspension in an alkaline fluid of the finely divided fat and nitrogenous matter introduce more of them than could be effected were they in a solid form. The fat is the germ of new cellular growth, and the nitrogenous matter is by the new cells formed into flesh, which is doubling its bulk monthly. The phosphate of lime is required for the hardening bones, the chloride of sodium and the iron for the daily increasing amount of blood in circulation. Milk may be said to be still alive as it leaves the breast fresh and warm, and quickly becomes living blood in the infant’s veins. A very slight chemical change is requisite. Its frequent administration is demanded by the rapid absorption, and the absence of regular meals prevents the overloading of the delicate young stomach with more than it can hold at once,

The wsholesomest nutriment for the first six months is milk alone. A vigorous baby can indeed bear with im punity much rough usage, and often appears none the worse for a certain quantity of farinaceous food; but the majority do not get habituated to it, without an exhibition of dislike which indicates rebellion of the bowels.

To give judicious diet its fair chance the frame must be well protected from the cold; and just in proportion as the normal temperature of the body is maintained so does growth prosper, as is satisfactorily proved by experiments on the young of the lower animals.

It is only when the teeth are on their way to the front, as shown by dribbling, that the parotid glands secrete an active saliva capable of digesting bread stuffs. Till then anything but milk must be given tentatively, and considered in the light of a means of education for its future mode of nutrition. Among the varieties of such means, the most generally applicable are broth and beef tea, at first pure, and then thickened with tapioca and arrowroot. Chicken soup, made with a little cream and sugar, serves as a change. Baked flour, biscuit powder, tops and bottoms, should all have their turn; change is necessary in the imperfect dietary which art supplies, and for change the stomach should be prepared by habit.

The consequences of premature weaning are insidious. The external aspect of the child is that of health, its muscles are strong, but the bones do hot harden in proportion, and if it tries to walk its limbs give way, and it is said to be suffering from rachitis or “rickets.”

These consequences follow in other animals as surely as in the human race; and in them it was possible to make the experiment crucial. A gentleman named Guérin set himself to find if he could produce rickets at will. He took a number of puppies in equally good condition, and having let them suckle for a time, he suddenly weaned half of them and fed them on raw meat, a fare which at first thoughtwouldseemthe mostsuitable for carnivorous animals. Nevertheless^ after a short time, those which continued to take the mother’s milk had grown strong and hearty, whilst those which had been treated with a more substantial dietary pined, and frequently threw up their victuals, then their limbs bent, and at the end of about four months they showed all the symptoms of confirmed rickets. From these experiments we must conclude that the rachitis depended mainly on the derangements of nutrition brought on by improper diet. A diet which is taken at a wrong season may fairly be called improper. For carnivora, it is flesh before the age of suckling has passed; for herbivora (and an experiment bearing on the point has been made on pigs), it is vegetable feeding begun when they ought to be at the teat.

The time for weaning should be fixed partly by the child’s age, partly by the growth of the teeth. The troubles to which children are subject at this crisis are usually gastric, such as are induced by summer weather; therefore at that season the weaning should be postponed, whereas in winter it should be hurried forward. The first group of teeth nine times out of ten consists of the lower central front teeth, which may appear any time during the sixth and seventh month. The mother may then begin to diminish the number of suckling times; and by a month she can have reduced them to twice a day, so as to be ready when the second group makes its way through the upper front gums to cut off the supply altogether. The third group, the lateral incisors and first grinders, usually after the first anniversary of birth give notice that solid food can be chewed. But it is prudent to let dairy milk form a considerable portion of the fare till the eye teeth are cut, which seldom happens till the eighteenth or twentieth month. At this period children are liable to diarrhoea, convulsions, irritation of the brain, rashes, and febrile catarrhs. In such cases it is often advisable to resume a complete milk diet, and sometimes a child’s life has been saved by its reapplication to the breast. These means are most feasible when the patient is accustomed to milk; indeed, if not, the latter expedient is hardly possible.

Diet in Childhood and Youth.— At this stage of life the diet must obviously be the best, which is a transition from that of infancy to that of adult age. Growth is not completed, but yet entire surrender of every consideration to the claim of growth is not possible, nor indeed desirable. Moreover that abundance of adipose tissue, or reserve new growth, which a baby can bear, is an impediment to the due education of the muscles of the boy or girl. The supply of nutriment needs not to be so continuous as before, but at the same time should be more frequent than for the adult. Up to at least fourteen or fifteen years of age the rule should be four meals a day, varied indeed, but nearly equal in nutritive power and in quantity, that is to say, all moderate, all sufficient. The maturity the body then reaches involves a hardening and enlargement of the bones and cartilages, and a strengthening of the digestive organs, which in healthy young persons enables us to dispense with some of the watchful care bestowed upon their diet. Three full meals a day are generally sufficient, and the requirements of mental training may be allowed to a certain extent to modify the attention to nutrition which has hitherto been paramount. But it must not be forgotten that the changes in figure and in internal organs are not completed till several years have passed, and that they involve increased growth and demand full supplies. As less bulky food is used, care should be taken that it is sufficiently nutritious, and habits should be acquired which conduce to making the most of it for the maintenance of strength.

The nutritiousness of food depends on digestibility and concentration. Food is digestible wshen it yields readily its constituents to the fluids destined for their reduction to absorbable chyme. It is more or less concentrated, according as a given w eight contains more or less matter capable of.supporting life. The degree in which they possess these qualifications united constitutes the absolute nutritive value of alimentary matters.

The degree of cohesion in the viands influences digestibility. Tough articles incapable of * being completely ground up by the teeth, remain unused, while fluids and semifluids lead the van of digestibles. The tissues of young vegetables and young animals are for this reason more digestible than old specimens. It is desirable also that the post mortem rigidity, which lasts several days in most instances, should have merged into softness before the meat is cooked, or should have been anticipated by cooking before the flesh is cold. In warm climates and exceptionally warm weather the latter course is the preferable. The dietician, especially when the feeding of the young is in question, will prefer those methods of culinary preparation which most break up the natural cohesion of the viands. And it may be noticed that the force of cohesion acts in all directions, and that it is no advantage for an article to be laterally friable if it remains stringy in a longitudinal direction.

Fat interposed between the component parts of food diminishes its digestibility. It is the interstitial fat between the fasciculi of muscular fibre in beef which rendersit to young persons and to dyspeptics less digestible than mutton.

A temperature above that of the body retards digestion. Meat, which is digested by the gastric juice in the stomach, has time to cool before it gets there; but farinaceous food, which depends for its conversion into chyme on the salivary glands, suffers a serious loss if by reason of being too hot it cannot avail itself of the saliva supplied by the mouth. It should also be borne in mind that a temperature much above that of the body cracks the enamel of the teeth.

Excessive concentration impairs digestibility. The principal medium by which nutriment is carried through the absorbent membrane of the digestive canal is water. There is no doubt it passes more rapidly by endosmosis than anything else. The removal, then, of water is an injury to viands, and drying, salting, over-frying, over roasting, and even over-boiling renders them less soluble in the digestive juices, and so less nutritious. A familiar illustration of this may be taken from eggs. Let an egg be lightly boiled, poached in water, custarded, or raw, and the stomach even of an invalid can bear it; but let it be baked in a pudding which requires a hot oven, or boiled hard, or otherwise submitted to a high temperature for a prolonged period, and it becomes a tasteless, leathery substance, which can be of no more use in the stomach than so much skin or hair. It is obvious then that it is mainly in a commercial point of view that articles of diet can'be called nutritious in proportion to their concentration. About this there can be no question; milk adulterated from the pump is worth so much less than pure milk, and a pound of beef steak sustains a man longer than a pint of veal broth.

Tiιe attainment of nutritiousness by concentration is of considerable importance to travellers and in military medicine. There are not a few strategists who attribute the success of the Germans in the war of 1870 to the easily carried and easily prepared food supplied to them by the sausage-makers of Berlin. Concentration of viands carried to excess, so as to be likely to affect the health, is usually made manifest by a diminution in the secretion of urine and itscondensed condition; while, on the other hand, if dilution is needlessly great, the action of the kidneys is excessive. Now the urine of young persons is naturally of lower specific gravity, that is, more aqueous, than that of adults. If it is found to equal in density the excretion of full growth, or if it is observed to be voided but rarely, the meals should be made more bulky, or better still, more frequent, so as not to overload the stomach.

An over-concentrated diet often induces costiveness. This should be counteracted by green vegetables and other dilute appetizing dishes, and never by purgative drugs. The habit of taking a considerable quantity and variety of fresh green vegetables has the further advantage of preventing that tendency to minor developments of scurvy which is not uncommonly found in youths nourished mainly on animal food. A softness or friability of the gums is one of the first signs of this. If the mouth bleeds after the application of a tooth brush, the use of fresh vegetables at every meal should be enforced,

The young are peculiarly liable to be affected by poisons conveyed in fluids. Their sensitive frames absorb quickly, and quickly turn to evil account such substances, even when diluted to au extent which makes them harmless to adults. The water therefore with which families, and still more with which schools are supplied, should be carefully subjected to analysis. Wherever a trace of lead is found, means should be adopted to remove the source of it; and organic products should have their origin clearly accounted for, and all possibility of sewage contamination excluded. These precautions are essential, in spite of the grown-up portion of the household having habitually used the water without injury.

Fresh milk has long had a bad popular reputation as occasionally conveying fever, and in some parts of Ireland the peasantry can hardly ever be got to take it “raw.” This is quite irrespective of the state of the cattle which furnish it; no cases of disease thus communicated have ever been traced home to sick cows. It is probably always due either to adulteration with dirty water, or to the vessels being washed in that dangerous medium, or to their being exposed to air loaded with elements of contagion.

Up to the period of full development the daily use of wine should be allowed only during illness and the express attendance of a medical adviser. Its habitual consumption by healthy children hastens forward the crisis of puberty, checks growth, and habituates them to the artificial sensation induced by alcohol.

Diet for Bodily Labour. —It seems certain that the old theory of Liebig, which attributed the whole of the force exhibited in muscular movements to the oxidation of muscular tissue, is untenable. There is not enough of the material oxidized, that is to say, destroyed and carried away as urea and other nitrogenous excretions, to generate so much force, as measured by the method of Joule. On the other hand, Traube goes too far when he would make out that in the performance of muscular work the metamorphosis of the organized constituents of contractile tissue is not involved, and that non-nitrogenous substances alone are consumed. The prolonged feats of walking performed by the pedestrian Weston in 1876 vastly increased the amounts excreted of those elements of the urine which are derived from the oxidation of muscle and nerve. The urea formed by the destructive assimilation of contractile fibre, and the phosphates whose main source is nervous tissue, were each nearly doubled during and shortly after the extraordinary strain upon those parts of the body. As might be expected, the machinery wears away quicker when it is harder worked, and requires to be repaired immediately by an enhanced quantity of new material, or it will be worn beyond the power of repair. The daily supply, therefore, of digestible nitrogenous food, meat par excellence, must be increased whenever the muscular exercise is increased. In making the recent extension of railways in Sicily, the progress was retarded by the slack work done by the Sicilian navvies compared with that got through by the English gangs. The former took scarcely any meat, preferring to save the wages expended by their comrades in that way. The idea occurred to the contractor of paying the men partly in money and partly in meat; and the result was a marked increase in the amount of work executed, which was brought nearly up to the British average. A mixed diet, with an increase in the proportionate quantity of meat when extra corporeal exertion is required, is the wholesomest, as well as the most economical, for all sorts of manual labourers.

It is absolutely essential that the fleshly machinery for doing work should be continuously replaced by flesh food, as it becomes worn out. Nitrogenous aliment after a few chemical changes replaces the lost muscle which has passed away in the excretions; just as the engineer makes ore into steel and renews the corroded boiler plate or thinned piston. Now, as the renewal of the plate or piston is a “stimulus” to the augmented performances of the engine, so meat is a “stimulus” to augmented muscular action. Taken in a digestible form during exertion, it allows the exertion to be continued longer, with greater ease and less consequent exhaustion. According to the testimony of soldiers experimentally put through forced marches of twenty miles a day, with loads of half a hundredweight each, “meatextract” bears away the palm from the other reputed stimulants commonly compared with it (viz., rum and coffee). “It does not put a spirit into you for a few miles only, but has a lasting effect; if I were ordered for continuous marching, and had my choice, I would certainly take the meat extract,” said an unprejudiced sergeant to Dr Parkes, who was the conductor of the experiments alluded to.

When the continuous repair of the muscular machinery is fully secured, the production of heat and force is most readily provided for by vegetable aliment, by reason of the large proportion of carbon which it contains. In assigning their physiological functions to the several sorts of food, nearly all the business of begetting active force should ap patently be ascribed to the solid hydrocarbons, starch and fat, by their conversion into carbonic acid. It is not necessary to be acquainted with every step of the process, which in the body we confessedly are not, to appreciate the argument. It is clearly important that these elements of diet should be furnished in sufficient quantity and in a digestible form. In additions to diet made in consequence of additional bodily work not only should the stimulus of animal food be attended to, but the bulk of starch and fat in the rations should be augmented even in larger proportion, for these aliments are the most direct contributors of force.

“Training” for athletic sports is based on the principles above enunciated. The usual time allotted to it is six weeks, and the objects to be attained in this period may be described as— [table]

The first is aimed at by considerably adding to the daily amount of nitrogenous and by diminishing farinaceous and liquid food, and providing that it should be so consumed as to be fully digested. The second and third are secured by gradually increasing the demands made upon the muscles, till they have learnt to exert at will all the powers of which they are capable, and...