With respect to the fatty substances which enter into the composition of our food, we would remark that they are not merely heat producers, but that they play a very important part in the process of digestion, not only increasing and accelerating greatly the digestibility of nitrogenous articles of food, but also aiding in the formation of bile.

Again, the starch is converted in the system into glucose, which is carried by the blood to the lungs, where it is split up into carbonic acid and water, as already described. Another product of the oxidation of starch and sugar is lactic acid, an important constituent of the gastric juice.

Starch, sugar, and fat have the following formulæ and percentage composition :

The mineral constituents of the body are not less necessary than the albuminates, fat, and the carbo-hydrates, and equally require to be renewed in the food consumed. Thus, sulphur and phosphorus are constantly present, combined chiefly with the albuminates. Phosphate of lime is found principally in the bones, teeth, and growing cells and tissues; phosphate of potash in the tissues, cells, and blood—the latter fluid is particularly rich in basic phosphate of potash, which forms by far the largest portion of its mineral constituents; chloride of sodium in the liquids, iron in the blood, and, lastly, carbonic, lactic, tartaric, acetic, and some other acids, which are converted in the system into carbonic acid, are requisite to maintain the alkalinity of the body, the absence of which gives rise to scurvy.

The function of chloride of sodium, or common salt, is but ill understood. It has been asserted that it is necessary for the assimilation of the food, but this seems not to be the case. Salt, in fact, is considered by some to be quite a superfluous addition to most of our articles of food, and nothing more than a condiment. It does not enter into the composition of any of the tissues, but is thrown out of the system in the excretions; and it has been repeatedly shown that some tribes of natives of Africa do not know the use of salt at all, and consider it a luxury and delicacy.

Iron is a most important constituent of the blood ; the colouring matter of the red corpuscles contains it in chemical combination. It is said to assist in the oxygenation of the blood.

Again, the imbibition of a large quantity of water daily is likewise a necessity, in order to endow many of the constituents of the foodespecially the albuminates—with certain physical properties, to render them plastic, soluble, or the more readily reducible to a state of solution; thus aiding absorption, nutrition, and elimination.

To sum up then, there is between the composition of the body and the food consumed, whether animal or vegetable, the closest possible resemblance.

Having thus enumerated the various kinds of food required to sustain the body in health, we have to consider the quantities needed. It will be obvious from what has already been advanced, that the quantities will vary, being dependent upon age, weight, muscular exertion, climate, &c.; but it has been determined by numerous independent inquiries, that the food daily consumed by an adult man of average weight-140 lb.—and in moderate work, should contain about the following quantities of the several classes of food, the figures given being those of Moleschott, quoted by Parkes in his admirable work on • Practical Hygiene,' and which figures should be generally adopted, in order to save the multiplication of sums and calculations :

:

One ounce of dry albuminate contains 69 grains of nitrogen and 234 of carbon; 1 ounce of dry fat, 3360 grains of carbon, and the same weight of either of the carbo-hydrates, starch or sugar, 194.2 grains ; or 100 grains of albuminates contain 15.8 of nitrogen and 53-5 of carbon; fat, 76.8 grains of carbon, and starch and sugar 44:4 grains.

But water to the extent of between 50 and 60 per cent. is contained in the food consumed, raising the amount to about 40 ounces.

Now, nearly the whole of the nitrogen and carbon contained in the chief articles of our food may be thus divided and distributed :

16 oz., less one-fifth bone, 14.4 Lean raw meat

cooked, about 8 oz. Fat of meat

ounce. Egg

2
Cheese

1
Butter
Bread.
Potatoes
Other vegetables
Milk
Sugar

99

18 16 8 2

Having thus arrived approximately at the quality and quantity of the several kinds of food required by an adult man of average size and weight, and in moderate work, it next becomes important to explain how each person may calculate for himself, and so ascertain the nutritive quality of his own, or any other, dietary. This important object may be accomplished by the help of the following table, taken, with one exception, from the work of Dr. Parkes, before quoted:

The use of the above table is exceedingly simple. Thus, the quantity by weight of any of the articles enumerated being known, the amounts of the albuminates, fats, and carbo-hydrates are easily calculated by a simple rule-of-three sum. Thus, supposing the allowance is 12 oz. of meat, one-fifth must be deducted for bone; the water in remain75 x 9.6 100

ing 9-6 oz. will be ascertained as follows: the other constituents.

=

7.2; and so on for

6

A few words in conclusion may be bestowed on the relative digestibility of different articles of food.

It appears from Dr. Beaumont's experiments on Alexis St. Martin that animal food is digested sooner than farinaceous, and, possibly, meat might therefore replace more quickly the wasted nitrogenous tissue than bread or peas; and it may be true, as asserted, that the change of tissue is more quick in meat-eaters, who require, therefore, more frequent supplies of food.'

• Rice, tripe, whipped eggs, sago, ta pioca, barley, boiled milk, raw eggs, lamb, parsnips, mashed and baked potatoes, and fricasseed chicken, are the most easily digested substances in the order here given, the rice disappearing from the stomach in one hour, and the fricasseed chicken in 24 hours. Beef, pork, mutton, oysters, butter, bread, veal, boiled and roast fowls are rather less digestible, roast beef disappearing from the stomach in three hours, and roast fowl in four hours. Salt beef and pork disappeared in 41 hours.'-- Parkes.

The admixture of the different classes of food aids digestibility, and fat taken with meat helps the digestion of the meat.

* According to the best writers on diet, it is not enough to give the proximate dietetic substances in proper amount. Variety must be introduced into the food, and different substances of the same class must be alternately employed. It may appear singular that this should be necessary; and certainly many men and most animals have perfect health on a very uniform diet. Yet there appears no doubt of the good effect of variety, and its action is probably on primary digestion. Sameness cloys; and with variety more food is taken, and a larger amount of nutriment is introduced. It is impossible, with rations, to introduce any great variety of food; but the same object appears to be secured by having a variety of cooking.”—Parkes.

CHAPTER II,

ON THE PRESERVATION OF FOOD.

It will be desirable before entering on the question of the adulteration of food to devote a short chapter to the subject of the various methods employed for its preservation. The methods resorted to are exceedingly numerous, and many of them have been patented on account of their supposed commercial'importance, but they may beall referred to the following heads :—to preservation by temperature, including an elevation of temperature, resulting in more or less complete cooking, and a reduction of temperature, as by freezing; by the exclusion of air, as when animal and vegetable substances are enclosed in hermeticallysealed tins; by coating the surface, as by paraffin, or when an artificial coating is formed by the coagulation of the albumen by plunging it into hot water; by immersing or mixing the substances to be preserved with a material which acts in the preservation mainly by the exclusion of air, as syrup or sugar; by compression, which serves to exclude the air partially, as also to remove superfluous moisture ; by the extraction of certain principles of meat by means of water, and the subsequent inspissation of the extract; by the use of various antiseptic substances, as alcohol, acetic acid, salt, saltpetre, alum, creosote, and charcoal ; by the employment of certain ncids and gases, as sulphurous acid and the sulphites, especially sulphite of soda, which retard decomposition by combining with the orygen of the air, which, in spite of all precautions, cannot be altogether excluded from the preserved material ; by carbonic acid, which acts by exclusion of the air, and the substitution of an atmosphere unfavourable to decomposition.

In many cases more than one of the above agencies are at work in the preservation of the food, as for example in tinned meats, in which not only is the air excluded, but the albumen of the meat is coagulated by cooking; in preserved milk, in which the greater part of the water is removed by evaporation, the albumen coagulated by the heat employed, and the air partially excluded by the addition of powdered sugar.

We will now give some brief examples illustrative of each of the methods of preservation above referred to.

Elevation of temperature.—Heat is employed for the double purpose of partially cooking the materials to be preserved, whereby the