TABLE I.--_Percentage Composition of some Common Food Materials.__Encyclopaedia Britannica, 11th Edition, "Diameter" to "Dinarchus" Volume 8, Slice 4

+--------------------------+--------+--------+---------+------+---------+--------+-----------+

+--------------------------+--------+--------+---------+------+---------+--------+-----------+

| | | | | | | | |

| | % | % | % | % | % | % | Calories. |

| Chuck | 16.3 | 52.6 | 15.5 | 15.0 | . . | 0.8 | 910 |

| Loin | 13.3 | 52.5 | 16.1 | 17.5 | . . | 0.9 | 1025 |

| Ribs | 20.8 | 43.8 | 13.9 | 21.2 | . . | 0.7 | 1135 |

| Round | 7.2 | 60.7 | 19.0 | 12.8 | . . | 1.0 | 890 |

| Shoulder | 16.4 | 56.8 | 16.4 | 9.8 | . . | 0.9 | 715 |

|Beef, dried and smoked | 4.7 | 53.7 | 26.4 | 6.9 | . . | 8.9 | 790 |

| Leg | 14.2 | 60.1 | 15.5 | 7.9 | . . | 0.9 | 625 |

| Loin | 16.5 | 57.6 | 16.6 | 9.0 | . . | 0.9 | 685 |

| Breast | 21.3 | 52.0 | 15.4 | 11.0 | . . | 0.8 | 745 |

| Leg | 18.4 | 51.2 | 15.1 | 14.7 | . . | 0.8 | 890 |

| Loin | 16.0 | 42.0 | 13.5 | 28.3 | . . | 0.7 | 1415 |

| Flank | 9.9 | 39.0 | 13.8 | 36.9 | . . | 0.6 | 1770 |

| Loin | 19.7 | 41.8 | 13.4 | 24.2 | . . | 0.8 | 1245 |

| Ham, fresh | 10.7 | 48.0 | 13.5 | 25.9 | . . | 0.8 | 1320 |

| Ham, smoked and salted | 13.6 | 34.8 | 14.2 | 33.4 | . . | 4.2 | 1635 |

| Fat, salt | . . | 7.9 | 1.9 | 86.2 | . . | 3.9 | 3555 |

| Bacon | 7.7 | 17.4 | 9.1 | 62.2 | . . | 4.1 | 2715 |

| Lard, refined | . . | . . | . . |100.0 | . . | . . | 4100 |

|Chicken | 25.9 | 47.1 | 13.7 | 12.3 | . . | 0.7 | 765 |

|Turkey | 22.7 | 42.4 | 16.1 | 18.4 | . . | 0.8 | 1060 |

|Goose | 17.6 | 38.5 | 13.4 | 29.8 | . . | 0.7 | 1475 |

|Eggs | 11.2 | 65.5 | 13.1 | 9.3 | . . | 0.9 | 635 |

|Cod, fresh | 29.9 | 58.5 | 11.1 | 0.2 | . . | 0.8 | 220 |

|Cod, salted | 24.9 | 40.2 | 16.0 | 0.4 | . . | 18.5 | 325 |

|Mackerel, fresh | 44.7 | 40.4 | 10.2 | 4.2 | . . | 0.7 | 370 |

|Herring, smoked | 44.4 | 19.2 | 20.5 | 8.8 | . . | 7.4 | 755 |

|Salmon, tinned | . . | 63.5 | 21.8 | 12.1 | . . | 2.6 | 915 |

|Oysters, shelled | . . | 88.3 | 6.0 | 1.3 | 3.3 | 1.1 | 225 |

|Butter | . . | 11.0 | 1.0 | 85.0 | . . | 3.0 | 3410 |

|Cheese | . . | 34.2 | 25.9 | 33.7 | 2.4 | 3.8 | 1885 |

|Milk, whole | . . | 87.0 | 3.3 | 4.0 | 5.0 | 0.7 | 310 |

|Milk, skimmed | . . | 90.5 | 3.4 | 0.3 | 5.1 | 0.7 | 165 |

|Oatmeal | . . | 7.7 | 16.7 | 7.3 | 66.2 | 2.1 | 1800 |

|Corn (maize) meal | . . | 12.5 | 9.2 | 1.9 | 75.4 | 1.0 | 1635 |

|Rye flour | . . | 12.9 | 6.8 | 0.9 | 78.7 | 0.7 | 1620 |

|Buckwheat flour | . . | 13.6 | 6.4 | 1.2 | 77.9 | 0.9 | 1605 |

|Rice | . . | 12.3 | 8.0 | 0.3 | 79.0 | 0.4 | 1620 |

|Wheat flour, white | . . | 12.0 | 11.4 | 1.0 | 75.1 | 0.5 | 1635 |

|Wheat flour, graham | . . | 11.3 | 13.3 | 2.2 | 71.4 | 1.8 | 1645 |

|Wheat, breakfast food | . . | 9.6 | 12.1 | 1.8 | 75.2 | 1.3 | 1680 |

|Wheat bread, white | . . | 35.3 | 9.2 | 1.3 | 53.1 | 1.1 | 1200 |

|Wheat bread, graham | . . | 35.7 | 8.9 | 1.8 | 52.1 | 1.5 | 1195 |

|Rye bread | . . | 35.7 | 9.0 | 0.6 | 53.2 | 1.5 | 1170 |

|Biscuit (crackers) | . . | 6.8 | 9.7 | 12.1 | 69.7 | 1.7 | 1925 |

|Macaroni | . . | 10.3 | 13.4 | 0.9 | 74.1 | 1.3 | 1645 |

|Sugar | . . | . . | . . | . . | 100.0 | . . | 1750 |

|Starch (corn starch) | . . | . . | . . | . . | 90.0 | . . | 1680 |

|Beans, dried | . . | 12.6 | 22.5 | 1.8 | 59.6 | 3.5 | 1520 |

|Peas, dried | . . | 9.5 | 24.6 | 1.0 | 62.0 | 2.9 | 1565 |

|Beets | 20.0 | 70.0 | 1.3 | 0.1 | 7.7 | 0.9 | 160 |

|Cabbage | 50.0 | 44.2 | 0.7 | 0.2 | 4.5 | 0.4 | 100 |

|Potatoes | 20.0 | 62.6 | 1.8 | 0.1 | 14.7 | 0.8 | 295 |

|Sweet potatoes | 20.0 | 55.2 | 1.4 | 0.6 | 21.9 | 0.9 | 440 |

|Tomatoes | . . | 94.3 | 0.9 | 0.4 | 3.9 | 0.5 | 100 |

|Apples | 25.0 | 63.3 | 0.3 | 0.3 | 10.8 | 0.3 | 190 |

|Bananas | 35.0 | 48.9 | 0.8 | 0.4 | 14.3 | 0.6 | 260 |

|Grapes | 25.0 | 58.0 | 1.0 | 1.2 | 14.4 | 0.4 | 295 |

|Strawberries | 5.0 | 85.9 | 0.9 | 0.6 | 7.0 | 0.6 | 150 |

|Almonds | 45.0 | 2.7 | 11.5 | 30.2 | 9.5 | 1.1 | 1515 |

|Brazil nuts | 49.6 | 2.6 | 8.6 | 33.7 | 3.5 | 2.0 | 1485 |

|Chestnuts | 16.0 | 37.8 | 5.2 | 4.5 | 35.4 | 1.1 | 915 |

|Walnuts | 58.1 | 1.0 | 6.9 | 26.6 | 6.8 | 0.6 | 1250 |

+--------------------------+--------+--------+---------+------+---------+--------+-----------+

In some cases the subjects were at rest; in others they performed

varying amounts of external muscular work on an apparatus by means of

which the amount of work done was measured. In some cases they fasted,

and in others they received diets generally not far from sufficient to

maintain nitrogen, and usually carbon, equilibrium in the body. In these

experiments the amount of energy expended by the body as heat and as

external muscular work measured in terms of heat agreed on the average

very closely with the amount of heat that would be produced by the

oxidation of all the matter metabolized in the body. The variations for

individual days, and in the average for individual experiments as well,

were in some cases appreciable, amounting to as much as 6%, which is not

strange in view of the uncertainties in physiological experimenting; but

in the average of all the experiments the energy of the expenditure was

above 99.9% of the energy of the income,--an agreement within one part

in 1000. While these results do not absolutely prove the application of

the law of the conservation of energy in the human body, they certainly

approximate very closely to such demonstration. It is of course possible

that energy may have given off from the body in other forms than heat

and external muscular work. It is conceivable, for example, that

intellectual activity may involve the transformation of physical energy,

and that the energy involved may be eliminated in some form now unknown.

But if the body did give off energy which was not measured in these

experiments, the quantity must have been extremely small. It seems fair

to infer from the results obtained that the metabolism of energy in the

body occurred in conformity with the law of the conservation of energy.

3. _Composition of Food Materials._--The composition of food is

determined by chemical analyses, the results of which are conventionally

expressed in terms of the nutritive ingredients previously described. As

a result of an enormous amount of such investigation in recent years,

the kinds and proportions of nutrients in our common sorts of food are

well known. Average values for percentage composition of some ordinary

food materials are shown in Table I. (Table I. also includes figures for

fuel value.)

It will be observed that different kinds of food materials vary widely

in their proportions of nutrients. In general the animal foods contain

the most protein and fats, and vegetable foods are rich in

carbohydrates. The chief nutrient of lean meat and fish is protein; but

in medium fat meats the proportion of fat is as large as that of

protein, and in the fatter meats it is larger. Cheese is rich in both

protein and fat. Among the vegetable foods, dried beans and peas are

especially rich in protein. The proportion in oatmeal is also fairly

large, in wheat it is moderate, and in maize meal and rice it is rather

small. Oats contain more oil than any of the common cereals, but in none

of them is the proportion especially large. The most abundant nutrient

in all the cereals is starch, which comprises from two-thirds to

three-fourths or more of their total nutritive substance. Cotton-seed is

rich in edible oil, and so are olives. Some of the nuts contain fairly

large proportions of both protein and fat. The nutrient of potatoes is

starch, present in fair proportion. Fruits contain considerable

carbohydrates, chiefly sugar. Green vegetables are not of much account

as sources of any of the nutrients or energy.

Similar food materials from different sources may also differ

considerably in composition. This is especially true of meats. Thus, the

leaner portions from a fat animal may contain nearly as much fat as the

fatter portions from a lean animal. The data here presented are largely

those for American food products, but the available analyses of English

food materials indicate that the latter differ but little from the

former in composition. The analyses of meats produced in Europe imply

that they commonly contain somewhat less fat and more water, and often

more protein, than American meats. The meats of English production

compare with the American more than with the European meats. Similar

vegetable foods from the different countries do not differ so much in

composition.

4. _Digestibility or Availability of Food Materials._--The value of any

food material for nutriment depends not merely upon the kinds and

amounts of nutrients it contains, but also upon the ease and convenience

with which the nutrients may be digested, and especially upon the

proportion of the nutrients that will be actually digested and

absorbed. Thus, two foods may contain equal amounts of the same

nutrient, but the one most easily digested will really be of most value

to the body, because less effort is necessary to utilize it.

Considerable study of this factor is being made, and much valuable

information is accumulating, but it is of more especial importance in

cases of disordered digestion.

TABLE II.--_Coefficients of Digestibility (or Availability) of

Nutrients in Different Classes of Food Materials._

+--------------------------+----------+----------+----------------+

+--------------------------+----------+----------+----------------+

| | | | |

| | % | % | % |

| Meats | 98 | 98 | .. |

| Fish | 96 | 97 | .. |

| Poultry | 96 | 97 | .. |

| Eggs | 97 | 98 | .. |

| Dairy products | 97 | 96 | 98 |

| mixed diet | 97 | 97 | 98 |

| Potatoes | 73 | .. | 98 |

| Beets, carrots, &c. | 72 | .. | 97 |

| Cabbage, lettuce, &c. | .. | .. | 83 |

| Legumes | 78 | 90 | 95 |

| Oatmeal | 78 | 90 | 97 |

| Corn meal | 80 | .. | 99 |

| Wheat meals without bran | 83 | .. | 93 |

| Wheat meals with bran | 75 | .. | 92 |

| White bread | 88 | .. | 98 |

| Entire wheat bread | 82 | .. | 94 |

| Graham bread | 76 | .. | 90 |

| Rice | 76 | .. | 91 |

| Fruits and nuts | 80 | 86 | 96 |

| Sugars and starches | .. | .. | 98 |

| mixed diet | 85 | 90 | 97 |

| Total food of mixed diet | 92 | 95 | 97 |

+--------------------------+----------+----------+----------------+

The digestibility of food in the sense of thoroughness of digestion,

however, is of particular importance in the present discussion. Only

that portion of the food that is digested and absorbed is available to

the body for the building of tissue and the production of energy. Not

all the food eaten is thus actually digested; undigested material is

excreted in the faeces. The thoroughness of digestion is determined

experimentally by weighing and analysing the food eaten and the faeces

pertaining to it. The difference between the corresponding ingredients

of the two is commonly considered to represent the amounts of the

ingredients digested. Expressed in percentages, these are called

coefficients of digestibility. See Table II.

Such a method is not strictly accurate, because the faeces do not

consist entirely of undigested food but contain in addition to this the

so-called metabolic products, which include the residuum of digestive

juices not resorbed, fragments of intestinal epithelium, &c. Since there

is as yet no satisfactory method of separating these constituents of the

excreta, the actual digestibility of the food is not determined. It has

been suggested that since these materials must originally come from

food, they represent, when expressed in terms of food ingredients, the

cost of digestion; hence that the values determined as above explained

represent the portion of food available to the body for the building of

tissue and the yielding of energy, and what is commonly designated as

digestibility should be called availability. Other writers retain the

term "digestibility," but express the results as "apparent

digestibility," until more knowledge regarding the metabolic products of

the excreta is available and the actual digestibility may be

ascertained.

Experimental inquiry of this nature has been very active in recent

years, especially in Europe, the United States and Japan; and the

results of considerably over 1000 digestion experiments with single

foods or combinations of food materials are available. These were mostly

with men, but some were with women and with children. The larger part of

these have been taken into account in the following estimations of the

digestibility of the nutrients in different classes of food materials.

The figures here shown are subject to revision as experimental data

accumulate. They are not to be taken as exact measures of the

digestibility (or availability) of every kind of food in each given

class, but they probably represent fairly well the average digestibility

of the classes of food materials as ordinarily utilized in the mixed

diet.

5. _Fuel Value of Food._--The potential energy of food is commonly

measured as the amount of heat evolved when the food is completely

oxidized. In the laboratory this is determined by burning the food in

oxygen in a calorimeter. The results, which are known as the heat of

combustion of the food, are expressed in calories, one calory being the

amount of heat necessary to raise the temperature of one kilogram of

water one degree centigrade. But it is to be observed that this unit is

employed simply from convenience, and without implication as to what

extent the energy of food is converted into heat in the body. The unit

employed in the measurement of some other form of energy might be used

instead, as, for example, the foot-ton, which represents the amount of

energy necessary to raise one ton through one foot.

TABLE III.--_Estimates of Heats of Combustion and of Fuel Value of

Nutrients in Ordinary Mixed Diet._

+---------------------------+-------------+-------------+

| Nutrients. | Heat of | Fuel Value. |

| | Combustion. | |

+---------------------------+-------------+-------------+

| | | |

| | Calories. | Calories. |

| | | |

| One gram of protein | 5.65 | 4.05 |

| One gram of fats | 9.40 | 8.93 |

| One gram of carbohydrates | 4.15 | 4.03 |

| | | |

+---------------------------+-------------+-------------+

The amount of energy which a given quantity of food will produce on

complete oxidation outside the body, however, is greater than that

which the body will actually derive from it. In the first place, as

previously shown, part of the food will not be digested and absorbed.

In the second place, the nitrogenous compounds absorbed are not

completely oxidized in the body, the residuum being excreted in the

urine as urea and other bodies that are capable of further oxidation

in the calorimeter. The total heat of combustion of the food eaten

must therefore be diminished by the heat of combustion of the

oxidizable material rejected by the body, to find what amount of

energy is actually available to the organism for the production of

work and heat. The amount thus determined is commonly known as the

fuel value of food.

Rubner's[7] commonly quoted estimates for the fuel value of the

nutrients of mixed diet are,--for protein and carbohydrates 4.1, and

for fats 9.3 calories per gram. According to the method of deduction,

however, these factors were more applicable to digested than to total

nutrients. Atwater[8] and associates have deduced, from data much more

extensive than those available to Rubner, factors for total nutrients

somewhat lower than these, as shown in Table III. These estimates seem

to represent the best average factors at present available, but are

subject to revision as knowledge is extended.

TABLE IV.--_Quantities of Available Nutrients and Energy in Daily

Food Consumption of Persons in Different Circumstances._

+------------------------------------------+--------+--------------------------------+

| | | Nutrients and Energy |

| | of +------+------+--------+---------+

+------------------------------------------+--------+------+------+--------+---------+

| | | | | | |

| English royal engineers | 1 | 132 | 79 | 612 | 3835 |

| Prussian machinists | 1 | 129 | 107 | 657 | 4265 |

| Swedish mechanics | 5 | 174 | 105 | 693 | 4590 |

| Bavarian lumbermen | 3 | 120 | 277 | 702 | 6015 |

| American lumbermen | 5 | 155 | 327 | 804 | 6745 |

| Japanese rice cleaner | 1 | 103 | 11 | 917 | 4415 |

| Japanese jinrikshaw runner | 1 | 137 | 22 | 1010 | 5050 |

| Chinese farm labourers in California | 1 | 132 | 90 | 621 | 3980 |

| American athletes | 19 | 178 | 192 | 525 | 4740 |

| American working-men's families | 13 | 156 | 226 | 694 | 5650 |

| | | | | | |

| Bavarian mechanics. | 11 | 112 | 32 | 553 | 3060 |

| Bavarian farm labourers | 5 | 126 | 52 | 526 | 3200 |

| Russian peasants | .. | 119 | 31 | 571 | 3155 |

| Prussian prisoners | 1 | 117 | 28 | 620 | 3320 |

| Swedish mechanics. | 6 | 123 | 75 | 507 | 3325 |

| American working-men's families | 69 | 105 | 135 | 426 | 3480 |

| | | | | | |

| American artisans' families | 21 | 93 | 107 | 358 | 2880 |

| English tailors (prisoners) | 1 | 121 | 37 | 509 | 2970 |

| German shoemakers | 1 | 99 | 73 | 367 | 2629 |

| Japanese prisoners | 1 | 43 | 6 | 444 | 2110 |

| | | | | | |

| Japanese professional men. | 13 | 75 | 15 | 408 | 2190 |

| Japanese students | 8 | 85 | 18 | 537 | 2800 |

| Japanese military cadets | 11 | 98 | 20 | 611 | 3185 |

| German physicians | 2 | 121 | 90 | 317 | 2685 |

| Swedish medical students | 5 | 117 | 108 | 291 | 2725 |

| Danish physicians | 1 | 124 | 133 | 242 | 2790 |

| men and students | 51 | 98 | 125 | 411 | 3285 |

| | | | | | |

| Prussian prisoners | 2 | 90 | 27 | 427 | 2400 |

| Japanese prisoners | 1 | 36 | 6 | 360 | 1725 |

| Inmates of home for aged--Germany | 1 | 85 | 43 | 322 | 2097 |

| Inmates of hospitals for insane--America | 49 | 80 | 86 | 353 | 2590 |

| | | | | | |

| Prussian working people | 13 | 63 | 43 | 372 | 2215 |

| Italian mechanics | 5 | 70 | 36 | 384 | 2225 |

| American working-men's families | 11 | 69 | 75 | 263 | 2085 |

+------------------------------------------+--------+------+------+--------+---------+

The heats of combustion of all the fats in an ordinary mixed diet would

average about 9.40 calories per gram, but as only 95% of the fat would

be available to the body, the fuel value per gram would be (9.40 X 0.95

=) 8.93 calories. Similarly, the average heat of combustion of

carbohydrates of the diet would be about 4.15 calories per gram, and as

97% of the total quantity is available to the body, the fuel value per

gram would be 4.03. (It is commonly assumed that the resorbed fats and

carbohydrates are completely oxidized in the body.) The heats of

combustion of all the kinds of protein in the diet would average about

5.65 calories per gram. Since about 92% of the total protein would be

available to the body, the potential energy of the available protein

would be equivalent to (5.65 X 0.92 =) 5.20 calories; but as the

available protein is not completely oxidized allowance must be made for

the potential energy of the incompletely oxidized residue. This is

estimated as equivalent to 1.15 calories for the 0.92 gram of available

protein; hence, the fuel value of the total protein is (5.20 - 1.15 =)

4.05 calories per gram. Nutrients of the same class, but from different

food materials, vary both in digestibility and in heat of combustion,

and hence in fuel value. These factors are therefore not so applicable

to the nutrients of the separate articles in a diet as to those of the

diet as a whole.

6. _Food Consumption._--Much information regarding the food consumption

of people in various circumstances in different parts of the world has

accumulated during the past twenty years, as a result of studies of

actual dietaries in England, Germany, Italy, Russia, Sweden and

elsewhere in Europe, in Japan and other oriental countries, and

especially in the United States. These studies commonly consist in

ascertaining the kinds, amounts and composition of the different food

materials consumed by a group of persons during a given period and the

number of meals taken by each member of the group, and computing the

quantities of the different nutrients in the food on the basis of one

man for one day. When the members of the group are of different age,

sex, occupation, &c., account must be taken of the effect of these

factors on consumption in estimating the value "per man." Men as a rule

eat more than women under similar conditions, women more than children,

and persons at active work more than those at sedentary occupation. The

navvy, for example, who is constantly using up more nutritive material

or body tissue to supply the energy required for his muscular work needs

more protein and energy in his food than a bookkeeper who sits at his

desk all day.

In making allowance for these differences, the various individuals are

commonly compared with a man at moderately active muscular work, who is

taken as unity. A man at hard muscular work is reckoned at 1.2 times

such an individual; a man with light muscular work or a boy 15-16 years

old, .9; a man at sedentary occupation, woman at moderately active

muscular work, boy 13-14 or girl 15-16 years old, .8; woman at light

work, boy 12 or girl 13-14 years old, .7; boy 10-11 or girl 10-12 years

old, .6; child 6-9 years old, .5; child 2-5 years old, .4; child under 2

years, .3. These factors are by no means absolute or final, but are

based in part upon experimental data and in part upon arbitrary

assumption.

The total number of dietary studies on record is very large, but not all

of them are complete enough to furnish reliable data. Upwards of 1000

are sufficiently accurate to be included in statistical averages of food

consumed by people in different circumstances, nearly half of which have

been made in the United States in the past decade. The number of persons

in the individual studies has ranged from one to several hundred. Some

typical results are shown in Table IV.

7. _Quantities of Nutrients needed._--For the proper nourishment of the

body, the important problem is how much protein, fats and carbohydrates,

or more simply, what amounts of protein and potential energy are needed

under varying circumstances, to build and repair muscular and other

tissues and to supply energy for muscular work, heat and other forms of

energy. The answer to the problem is sought in the data obtained in

dietary studies with considerable numbers of people, and in metabolism

experiments with individuals in which the income and expenditure of the

body are measured. From the information thus derived, different

investigators have proposed so-called dietary standards, such as are

shown in the table below, but unfortunately the experimental data are

still insufficient for entirely trustworthy figures of this sort; hence

the term "standard" as here used is misleading. The figures given are

not to be considered as exact and final as that would suggest; they are

merely tentative estimates of the average daily amounts of nutrients and

energy required. (It is to be especially noted that these are available

nutrients and fuel value rather than total nutrients and energy.) Some

of the values proposed by other investigators are slightly larger than

these, and others are decidedly smaller, but these are the ones that

have hitherto been most commonly accepted in Europe and America.

TABLE V.--_Standards for Dietaries. Available Nutrients and Energy

per Man per Day._

+---------------------------+---------+--------+---------+---------+

+---------------------------+---------+--------+---------+---------+

| | | | | |

| Man at hard work | 133 | 95 | 437 | 3270 |

| Man at moderate work | 109 | 53 | 485 | 2965 |

| muscular work | 161 | ..[10]| ..[10]| 5500 |

| Man at hard muscular work | 138 | .. | .. | 4150 |

| active muscular work | 115 | .. | .. | 3400 |

| muscular work | 103 | .. | .. | 3050 |

| active work | 92 | .. | .. | 2700 |

| muscular exercise | 83 | .. | .. | 2450 |

| | | | | |

+---------------------------+---------+--------+---------+---------+

8. _Hygienic Economy of Food._--For people in good health, there are two

important rules to be observed in the regulation of the diet. One is to

choose the foods that "agree" with them, and to avoid those which they

cannot digest and assimilate without harm; and the other is to use such

sorts and quantities of foods as will supply the kinds and amounts of

nutrients needed by the body and yet to avoid burdening it with

superfluous material to be disposed of at the cost of health and

strength.

As for the first-mentioned rule, it is practically impossible to give

information that may be of more than general application. There are

people who, because of some individual peculiarity, cannot use foods

which for people in general are wholesome and nutritious. Some persons

cannot endure milk, others suffer if they eat eggs, others have to

eschew certain kinds of meat, or are made uncomfortable by fruit; but

such cases are exceptions. Very little is known regarding the cause of

these conditions. It is possible that in the metabolic processes to

which the ingredients of the food are subjected in the body, or even

during digestion before the substances are actually taken into the body,

compounds may be formed that are in one way or another injurious.

Whatever the cause may be, it is literally true in this sense that "what

is one man's meat is another man's poison," and each must learn for

himself what foods "agree" with him and what ones do not. But for the

great majority of people in health, suitable combinations of the

ordinary sorts of wholesome food materials make a healthful diet. On the

other hand, some foods are of particular value at times, aside from

their use for nourishment. Fruits and green vegetables often benefit

people greatly, not as nutriment merely, for they may have very little

actual nutritive material, but because of fruit or vegetable acids or

other substances which they contain, and which sometimes serve a most

useful purpose.

TABLE VI.--_Amounts of Nutrients and Energy Furnished for One

Shilling in Food Materials at Ordinary Prices._

+----------------------+-------+----------------------------------------------+

| | | One Shilling will buy |

| | +----------+-------------------------+---------+

| as Purchased. | per |Total Food+-------------------------+ Fuel |

+----------------------+-------+----------+--------+------+---------+---------+

| | s. d. | lb. | lb. | lb. | lb. |Calories.|

| Beef, round | 0 10 | 1.20 | .22 | .14 | .. | 1,155 |

| |0 8-1/2| 1.41 | .26 | .17 | .. | 1,235 |

| | 0 5 | 2.40 | .44 | .29 | .. | 2,105 |

| | | | | | | |

| Beef, sirloin | 0 10 | 1.20 | .19 | .20 | .. | 1,225 |

| | 0 9 | 1.33 | .21 | .22 | .. | 1,360 |

| | 0 8 | 1.50 | .. | .. | .. | .. |

| | 0 5 | 2.40 | .. | .. | .. | .. |

| | | | | | | |

| Beef, rib | 0 9 | 1.33 | .19 | .19 | .. | 1,200 |

| |0 7-1/2| 1.60 | .. | .. | .. | .. |

| |0 4-1/2| 2.67 | .. | .. | .. | .. |

| | | | | | | |

| Mutton, leg | 0 9 | 1.33 | .20 | .20 | .. | 1,245 |

| | 0 5 | 2.40 | .37 | .35 | .. | 2,245 |

| | | | | | | |

| Pork, spare-rib | 0 9 | 1.33 | .17 | .31 | .. | 1,645 |

| | 0 7 | 1.71 | .22 | .39 | .. | 2,110 |

| | | | | | | |

| Pork, salt, fat | 0 7 | 1.71 | .03 | 1.40 | .. | 6,025 |

| | 0 5 | 2.40 | .04 | 1.97 | .. | 8,460 |

| | | | | | | |

| Pork, smoked ham | 0 8 | 1.50 | .20 | .48 | .. | 2,435 |

| |0 4-1/2| 2.67 | .36 | .85 | .. | 4,330 |

| | | | | | | |

| Fresh cod | 0 4 | 3.00 | .34 | .01 | .. | 710 |

| | 0 3 | 4.00 | .45 | .01 | .. | 945 |

| | | | | | | |

| Salt cod |0 3-1/2| 3.43 | .54 | .07 | .. | 1,370 |

| | 0 10 | 1.20 | .07 | .01 | .04 | 275 |

| | | | | | | |

|Milk, whole, 4d. a qt.| 0 2 | 6.00 | .19 | .23 | .30 | 1,915 |

| " 3d. a qt.|0 1-1/2| 8.00 | .26 | .30 | .40 | 2,550 |

| " 2d. a qt.| 0 1 | 12.00 | .38 | .46 | .60 | 3,825 |

| | | | | | | |

| Milk, skimmed, 2d. a | 0 1 | 12.00 | .40 | .03 | .61 | 2,085 |

| qt. | | | | | | |

| Butter | 1 6 | .67 | .01 | .54 | .. | 2,320 |

| | 1 3 | .80 | .01 | .64 | .. | 2,770 |

| | 1 0 | 1.00 | .01 | .81 | .. | 3,460 |

| | | | | | | |

| Margarine | 0 4 | 3.00 | .. | 2.37 | .. | 10,080 |

| | | | | | | |

| Eggs, 2s. a dozen | 1 4 | .75 | .10 | .07 | .. | 475 |

| " 1-1/2s. a dozen | 1 0 | 1.00 | .13 | .09 | .. | 635 |

| " 1s. a dozen | 0 8 | 1.50 | .19 | .13 | .. | 950 |

| | | | | | | |

| Cheese | 0 8 | 1.50 | .38 | .48 | .04 | 2,865 |

| | 0 7 | 1.71 | .43 | .55 | .04 | 3,265 |

| | 0 5 | 2.40 | .60 | .77 | .06 | 4,585 |

| | | | | | | |

| Wheat bread |0 1-1/8| 10.67 | .76 | .13 | 5.57 | 12,421 |

| | | | | | | |

| Wheat flour |0 1-3/5| 7.64 | .67 | .07 | 5.63 | 12,110 |

| |0 1-1/2| 8.16 | .72 | .07 | 6.01 | 12,935 |

| | | | | | | |

| Oatmeal |0 1-2/5| 8.39 | 1.11 | .54 | 5.54 | 14,835 |

| |0 1-1/2| 8.16 | 1.08 | .53 | 5.39 | 14,430 |

| | | | | | | |

| Rice |0 1-3/4| 6.86 | .45 | .02 | 5.27 | 10,795 |

| | | | | | | |

| Potatoes |0 0-2/3| 18.00 | .25 | .02 | 2.70 | 5,605 |

| |0 0-1/2| 24.00 | .34 | .02 | 3.60 | 7,470 |

| | | | | | | |

| Beans | 0 2 | 6.00 | 1.05 | .10 | 3.47 | 8,960 |

| | | | | | | |

| Sugar | 1 3/4 | 6.86 | .. | .. | 6.86 | 12,760 |

+----------------------+-------+----------+--------+------+---------+---------+

The proper observance of the second rule mentioned requires information

regarding the demands of the body for food under different

circumstances. To supply this information is one purpose of the effort

to determine the so-called dietary standards mentioned above. It should

be observed, however, that these are generally more applicable to the

proper feeding of a group or class of people as a whole than for

particular individuals in this class. The needs of individuals will vary

largely from the average in accordance with the activity and

individuality. Moreover, it is neither necessary nor desirable for the

individual to follow any standard exactly from day to day. It is

requisite only that the average supply shall be sufficient to meet the

demands of the body during a given period.

The cooking of food and other modes of preparing it for consumption have

much to do with its nutritive value. Many materials which, owing to

their mechanical condition or to some other cause, are not particularly

desirable food materials in their natural state, are quite nutritious

when cooked or otherwise prepared for consumption. It is also a matter

of common experience that well-cooked food is wholesome and appetizing,

whereas the same material poorly prepared is unpalatable. There are

three chief purposes of cooking; the first is to change the mechanical

condition of the food. Heating changes the structure of many food

materials very materially, so that they may be more easily chewed and

brought into a condition in which the digestive juices can act upon them

more freely, and in this way probably influencing the ease and

thoroughness of digestion. The second is to make the food more

appetizing by improving the appearance or flavour or both. Food which is

attractive to the eye and pleasing to the palate quickens the flow of

saliva and other digestive juices and thus aids digestion. The third is

to kill, by heat, disease germs, parasites or other dangerous organisms

that may be contained in food. This is often a very important matter and

applies to both animal and vegetable foods. Scrupulous neatness should

always be observed in storing, handling and serving food. If ever

cleanliness is desirable it must be in the things we eat, and every care

should be taken to ensure it for the sake of health as well as of

decency. Cleanliness in this connexion means not only absence of visible

dirt, but freedom from undesirable bacteria and other minute organisms

and from worms and other parasites. If food, raw or cooked, is kept in

dirty places, peddled from dirty carts, prepared in dirty rooms and in

dirty dishes, or exposed to foul air, disease germs and other offensive

and dangerous substances may easily enter it.

9. _Pecuniary Economy of Food._--Statistics of economy and of cost of

living in Great Britain, Germany and the United States show that at

least half, and commonly more, of the income of wage-earners and other

people in moderate circumstances is expended for subsistence. The

relatively large cost of food, and the important influence of diet upon

health and strength, make a more widespread understanding of the subject

of dietetics very desirable. The maxim that "the best is the cheapest"

does not apply to food. The "best" food, in the sense of that which is

the finest in appearance and flavour and which is sold at the highest

price, is not generally the most economical.

The price of food is not regulated largely by its value for nutriment.

Its agreeableness to the palate or to the buyer's fancy is a large

factor in determining the current demand and market price. There is no

more nutriment in an ounce of protein or fat from the tender-loin of

beef than from the round or shoulder. The protein of animal food has,

however, some advantage over that of vegetable foods in that it is more

thoroughly, and perhaps more easily, digested, for which reason it would

be economical to pay somewhat more for the same quantity of nutritive

material in the animal food. Furthermore, animal foods such as meats,

fish and the like, gratify the palate as most vegetable foods do not.

For persons in good health, foods in which the nutrients are the most

expensive are like costly articles of adornment. People who can well

afford them may be justified in buying them, but they are not

economical. The most economical food is that which is at the same time

most healthful and cheapest.

The variations in the cost of the actual nutriment in different food

materials may be illustrated by comparison of the amounts of nutrients

obtained for a given sum in the materials as bought at ordinary market

prices. This is done in Table VI., which shows the amounts of available

nutrients contained in the quantities of different food materials that

may be purchased for one shilling at prices common in England.

When proper attention is given to the needs of the body for food and the

relation between cost and nutritive value of food materials, it will be

found that with care in the purchase and skill in the preparation of

food, considerable control may be had over the expensiveness of a

palatable, nutritious and healthful diet.

AUTHORITIES.--COMPOSITION OF FOODS:--Konig, _Chemie der menschlichen

Nahrungs- und Genussmittel_; Atwater and Bryant, "Composition of

American Food Materials," Bul. 28, Office of Experiment Stations, U.S.

Department of Agriculture. NUTRITION AND DIETETICS:--Armsby,

_Principles of Animal Nutrition_; Lusk, _The Science of Nutrition_;

Burney Yeo, _Food in Health and Disease_; Munk and Uffelmann, _Die

Ernahrung des gesunden und kranken Menschen_; Von Leyden,

_Ernahrungstherapie und Diatetik_; Dujardin-Beaumetz, Hygiene

alimentaire; Hutchison, _Food and Dietetics_; R. H. Chittenden,

_Physiological Economy in Nutrition_ (1904), _Nutrition of Man_

(1907); Atwater, "Chemistry and Economy of Food," Bul. 21, Office of

Experiment Stations, U.S. Department of Agriculture. See also other

Bulletins of the same office on composition of food, results of

dietary studies, metabolism experiments, &c., in the United States.

GENERAL METABOLISM:--Voit, _Physiologie des allgemeinen Stoffwechsels

und der Ernahrung_; Hermann, _Handbuch der Physiologie_, Bd. vi.; Von

Noorden, _Pathologie des Stoffwechsels_; Schafer, _Text-Book of

Physiology_, vol. i.; Atwater and Langworthy, "Digest of Metabolism

Experiments," Bull. 45, Office of Experiment Stations, U.S. Department

of Agriculture. (W. O. A.; R. D. M.)

Encyclopaedia Britannica, 11th Edition, "Diameter" to "Dinarchus" Volume 8, Slice 4 · 第 29 / 86 题