The calculations of Dr. PIay fair "on the food of man in relation to his useful work" 1 enable us, by another route, to arrive at an estimate of what amount of solid victuals is required by an adult living by bodily labor to preserve his health under various circumstances. The circumstances which chiefly affect the question can be classified thus: (1) bare existence; (2) moderate exercise; (3) active work; and (4) hard work.

1 Lectures delivered at the Royal Institution, London, April 28,1865.

1. The first is calculated from the mean of sundry prison dietaries, of the convalescents' diet at hospitals, that of London needlewomen, and of that supplied during the Lancashire cotton famine, as reported by Mr. Simon. The result is that, in a condition of low health, without activity, 2 1/4 ounces of nitrogenous food, 1 ounce of fat, 12 ounces of starch, and 1/4 of an ounce of mineral matters a day are necessary. The amount of carbon in this is equal to 7.44 ounces. In other words, a man's life will be shortened or burdened by disease in the future, or he will die of gradual starvation, unless his provision for a week is equivalent to three pounds of meat with one pound of fat on it, or with the same quantity of butter or lard, two quartern loaves of bread, and about an ounce of salt and other condiments. If he cannot get meat, he must supply its place with at least two extra quartern loaves, or about a stone and a half of potatoes, or between five and six pounds of oatmeal, unless he is, indeed, so fortunate as to be able to get skim milk, of which five pints a week will replace the meat.

A person reduced to bare existence diet can undertake no habitual toil, mental or bodily, under the penalty of breaking down.

"Bare existence" diet is that which requires to be estimated for administration to certain classes of the community who have a claim on their fellow-countrymen that their lives and health shall be preserved in statu quo, but nothing further. Such are prisoners, paupers, or the members of a temporarily famine-stricken community.

It would be obviously unjust to apply the same scale of quantity and quality to all persons under varying circumstances of constitution and outward surroundings; and to attempt to feed in the same way all these people for short or long periods, idle or employed, with light work or hard work, in hot or in cold weather, excited by hope or depressed by failure, involves an error of either excess or defect, or both at once. The dietaries recommended by the Home Office for prisoners very properly take all these circumstances into consideration. They allot "bare existence " diet only to those sentenced for short terms without labor. And they recognize the fact that a man's health is not injured (perhaps sometimes it is improved) by a few days of such abstinence as would in the long-run be deleterious to him. Under a sentence of seven days, a prisoner gets daily one pound of bread and a quart of gruel containing four ounces of oatmeal. For more than seven and under twenty-one days, he has an extra half pound of bread. For longer terms it is advised to add potatoes and meat.

The nutritive value of the first-named diet is thus calculated by Dr. Pavy ("Treatise on Food," page 415) :

Of the second:

In the convict establishments prisoners are all under long sentences, and are classified for dietetic purposes according to their occupation.

The sparest of all is called "punishment diet," and is administered for offenses against the internal discipline of the prison. It is equivalent to corporeal chastisement, being designed to make the stomach a source of direct pain. It is limited to a period of three days, and fully answers its purposed end as a deterrent by causing the solar plexus to experience the greatest amount of distress it is capable of; for after the expiration of that period sensation becomes blunted. It consists of one pound of bread and as much water as the prisoner chooses to drink. This last-named concession is not an unimportant one; for it has been already remarked that a supply of fluid enables starvation, and by implication abstinence, to be longer borne. At the same time, it probably postpones the anaesthesia, and therefore makes the intended suffering more real. "Punishment diet" contains, in Dr. Pavy's estimate:

This is about half of what an average man requires to sustain himself without work, and under its discipline he would probably lose three or four ounces of his weight daily till his bodily substance was reduced by six-tenths, at which period, according to Chossat's experiments, he would die.

"Penal diet" is that which is apportioned for more protracted punishment. It may be continued for three months. It consists of 20 ounces of bread, 8 ounces of oatmeal, 20 ounces of milk, and 16 ounces of potatoes daily. Its chemical constituents are as follows:

Upon this diet a fair amount of work may be done. The combustion of the carbohydrates evolves sufficient force to raise a ton 4,193 feet; and thus the effete muscular substance may be worn off by destructive assimilation, making place for new muscle derived from the nitrogenous matter, of which a bare sufficiency, but yet probably a sufficiency, is supplied. A man of strong constitution is usually found at the end of it to be in good health and of normal weight; yet he has never probably experienced the content which arises from a luxus consumption of food. It is intended to deny him the normal pleasure of the accumulation of reserve force in the gastric region. This pleasurable sensation under ordinary circumstances much promotes digestion, so that the whole of the ingesta are made the best use of; and therefore in "penal diet," as above quoted, it has been found expedient to introduce the slight excess to be noticed above what is needful to accomplish the required work in "foot-tons" (see before). The penalty of the regimen involves a certain degree of waste.