Many vegetables, and, in fact, all starch granules, contain proteid material which is chiefly used in the formation of outside coverings to afford protection and firmness of resistance to a softer pulp within. Neither is animal food strictly nitrogenous, on account of its fat and glycogen, nor is vegetable food strictly non-nitrogenous, owing to its albuminoids and other forms of proteids (such as plant albumin, found in the legumes, etc.), yet this classification is a very convenient and simple one which has met with general acceptance. It will be used in this book whenever a further degree of subdivision is not needed, but always with the understanding that it has only a general and not too literal application, and, unless otherwise distinctly specified, "nitrogenous food" will be understood to include animal food, and "non-nitrogenous food" to include vegetable food of all kinds, and vice versa.

Table Of Composition Of Some Common Foods (Hofmann)

Nitrogenous constituents.

Fat.

Carbohydrates.

Salts.

Total.

Fat beef

51.4

45.6

...

3.0

100

Lean beef

89.4

5.5

....

5.1

100

Pea flour

27.3

0.8

68.9

3.0

100

Wheat

16.6

0.9

81.9

0.6

100

Rice

7.7

0.4

9I.2

0.7

100

Table Of Composition Of Common Foods (Abridged From Parkes)

Articles.

Water.

Proteids.

Fats.

Carbohydrates.

Salts.

Beefsteak

74.4

20.5

3.5

1.6

Fat pork

39.0

9.8

48.9

....

2.3

Smoked ham

27.8

24.O

36.5

10.1

Whitefish

78.O

18.1

2.9

1.0

Polutry

74.0

2I.O

3.8

1.2

White wheat in bread

40.0

8.0

1.5

49.2

'•3

Biscuit

8.0

15.6

1.3

73.4

1.7

Oatmeal

15.0

12.6

5.6

63.0

3.0

Maize

13.5

10.0

6.7

64.5

1.4

Macaroni

13.1

9.0

0.3

76.8

0.8

Arrowroot

15.4

0.8

83.3

0.27

Peas (dry)

15.0

22.0

2.0

53.0

2.4

Potatoes

74.0

2.0

0.16

21.0

1.0

Carrots

85.0

1.6

0.25

8.4

1.0

Cabbages

91.0

1.8

5.0

5.8

0.7

Butter............................

6.0

0.3

91.0

2.7

egg (1-10 for shell)

73.5

13-5

11.6

1.0

Cheese

36.8

33 5

24.3

5.4

Milk (specific gravity, 1032)

86.8

4.0

3.7

4.8

0.7

Cream

66.0

2.7

26.7

2.8

1.8

Skimmed milk

88.0

4.0

1.8

5.4

0.8

Sugar

3.0

96.5

0.5

The foregoing analyses by Hofmann and Parkes of several common foods illustrate the mixed character of animal and vegetable foods and the difficulties of a purely chemical basis of classification.

For the purpose of the present work, it is convenient to subdivide foods by the following classification: I. Water; II. Salts; III. Proteids (chiefly albumins and the allied gelatin); IV. Starches; V. Sugars; VI. Fats and oils.

Protein is a comprehensive term used in food calculations to signify all nitrogenous food substances, except the nitrogenous fats. Proteids are nitrogenous substances of definite composition forming a portion of the protein class.

Some writers class oxygen in a separate division among foods. This seems unnecessary, unless a separate division is made for hydrogen, and in fact for each element. The primary object of food classification is to obtain a practical working basis of subdivision, and the less complex this is made, the better. Further details of grouping belong to the refinements of physiological or organic chemistry, and are out of place in the present work.