14. ORGANIC SUBSTANCES.--These substances are derived from the vegetable and animal creations. They comprise all those articles which are commonly spoken of as "food," and which are essential to sustain the body in life and strength. They are divided into three groups, namely: the Alb.u.minoid substances, the Fats, and Sugars.

[Sidenote: 15. The Alb.u.minoid cla.s.s, includes what? These compounds const.i.tute what? The food? Their importance? Their properties?]

15. THE ALb.u.mINOIDS.--This cla.s.s includes three important nutritive substances--(1) _Alb.u.men_, which gives it its name; (2) _Fibrin_, including _gluten_; and (3) _Casein_. These compounds const.i.tute a large part of the human body, and the food contains them in proportionally large quant.i.ties.

Their importance is so great, and the system so promptly suffers from their absence, that they have been styled the "_nutritious_ substances." The properties which they hold in common are, that they do not crystallize, and have a jelly-like form, except when heat is applied to them, when they harden, or _coagulate_. {58}

[Sidenote: 16. Decomposition? Effect of cold? Ill.u.s.trations? Elephants?]

16. They likewise decompose, or _putrefy_, under the influence of warmth and moisture. Hence the decay of all dead animal tissues. Cold arrests this process. It is well known that milk, eggs, and the like, "keep" much longer in winter than at other seasons. The bodies of elephants, caught in the ice many hundred years ago, are occasionally borne by the icebergs to the coast of Siberia, completely frozen, but preserved almost perfectly in form and limb.

[Sidenote: 17. In what substances does alb.u.men exist? What further is said of the egg?]

17. ALb.u.mEN exists in milk, meat, the grains, and the juices of many plants; but the purest form is obtained from the white of egg. When we consider that an egg is composed chiefly of alb.u.men and water--namely, six parts in seven; and when we also consider the numerous, diverse, and complex tissues--the muscles, bones, internal organs, bill, claws, and feathers--with which the chick is equipped on leaving his sh.e.l.l, we are impressed with the importance of these apparently simple const.i.tuents of the food and body.

[Sidenote: 18. Fibrin, gluten, clotting of the blood?]

18. FIBRIN is derived from meats, and exists in the blood both of man and the lower animals. _Gluten_, or vegetable fibrin, resembles closely true fibrin, and is abundantly furnished in wheat and other grains from which flour is commonly made. Animal fibrin coagulates spontaneously when it is removed from the body, and thus causes the "clotting" of the blood.

[Sidenote: 19. Casein? Its coagulation? Effect of rennet? Making of cheese?]

19. CASEIN is the curdy ingredient of milk, and a highly important food-substance. Its coagulation in milk takes place not from heat, but by the addition of an acid, and also when milk becomes sour from exposure to the air. It is commonly effected, however, by introducing a piece of _rennet_, a preparation made from a calf's stomach. The _curds_, or casein, may then be separated from the _whey_, {59} and made into cheese, by pressing it sufficiently to drive off the water.

[Sidenote: 20. What are the fats? The oils? How supplied? How alike?

Emulsifying? Example? How do we know it?]

20. THE FATS OR OILS.--This is the second group of organic foods. Those which are more solid are called _fats_: the more fluid ones are the _oils_.

Oleaginous substances are supplied in both animal and vegetable food; but, from whatever source derived, they are chemically much alike. They are insoluble in water, and yet they unite readily with the watery fluids of the body, and are by them conveyed to its various parts for their nourishment. This is due to their property of "emulsifying;" that is, they are held in suspension, in a finely divided state, in water. Ordinary milk is an example of an _emulsion_. We know that it contains fat; for b.u.t.ter is obtained from it, and, under the microscope, the minute oil-globules may be distinctly seen.

[Sidenote: 21. Whence are fatty articles of food derived?]

21. In our country and climate, and also in colder climates, fatty articles of food are princ.i.p.ally derived from the animal creation, such as meat or flesh, milk and b.u.t.ter. But most of the bread-stuffs contain more or less fat or oil; Indian meal as much as nine parts in a hundred.

[Sidenote: 22. Appet.i.te of persons in cold climates? What do they require?

Upon what must they rely? Why? The Esquimaux? Laplander? Olive and palm?]

22. Among persons living in cold climates, the appet.i.te for oleaginous food is especially eager; and they require large quant.i.ties of it to enable them to resist the depressing influences of cold. Since vegetation is scanty and innutritious, and the waters of the frozen regions abound in animal life, they must rely wholly upon a diet derived from the latter source. The Esquimaux consumes daily from ten to fifteen pounds of meat or blubber, a large proportion of which is fat. The Laplander will drink train-oil, and regards tallow-candles as a great delicacy. In hot climates, on the contrary, where flourish the olive {60} and the palm, this kind of food may be obtained from vegetable sources in abundant quant.i.ties.

[Sidenote: 23. Which are the third of the organic groups? What do they embrace? Points of resemblance?]

23. THE SUGARS, OR THE SACCHARINE SUBSTANCES.--These const.i.tute the third, and last, group of the organic substances, which are employed as food. This group embraces, in addition to the different kinds of _Sugar_, the varieties of starch and gum, from whatever source derived. The two substances last named do not, at first sight, present many points of similarity to sugar; but they closely resemble it in respect to their ultimate chemical composition, being made up of the same elements, in nearly the same proportions. And their office in the system is the same, since they are all changed into sugar by the processes of digestion.

[Sidenote: 24. Origin of the sugars? Ordinary sugar? Beetroot? Maple-sugar?

Grape-sugar? Cane-sugar?]

24. SUGAR is chiefly of vegetable origin; the animal varieties being obtained from honey and milk. The most noticeable characteristic of this substance is its agreeable, sweet taste, which makes it everywhere a favorite article of food. But this quality of sweetness is not possessed by all the varieties of sugar in the same degree; that obtained from milk, for instance, has a comparatively feeble taste, but rather imparts a gritty feeling to the tongue. The other important properties of sugar are, its power to crystallize when evaporated from watery solutions, such as the juices of many plants; a tendency to ferment, by which process alcohol is produced; and a ready solubility in water. This latter quality renders it very easy of digestion, and more so than any other of the saccharine group.

It is computed that the annual production of sugar, in all parts of the world, is more than one million of tons. The kind of sugar that is in ordinary use, in this country, is prepared from the juice of the sugar-cane, which contains eighteen per cent. of sugar. In France it is manufactured from the {61} beet root, which holds about nine per cent.; the maple-tree of our climate yields a similar sugar. The sweet taste of fruits is due to the presence of grape-sugar: the white grains seen on raisins belong to this variety. Cane-sugar is more soluble than the latter, and has twice the sweetening power.

[Ill.u.s.tration: FIG. 15.--GRANULES OF POTATO STARCH.]

[Sidenote: 25. Starch, how widely distributed? Its qualities? Its const.i.tuents? Its solubility?]

25. STARCH.--This is the most widely distributed of the vegetable principles. It is tasteless, inodorous, and does not crystallize. It consists of minute rounded granules, which, under the microscope, reveal a somewhat uniform structure (Fig. 15). Starch will not dissolve in cold water, but in boiling water the small grains burst open, and may then be dissolved and digested.

[Sidenote: 26. How much starch in bread-stuffs? In rice? Unripe fruits?

Ripe fruits?]

26. The bread stuffs, wheat, corn, and rye flours, are more than one-half starch. Rice, which is the "staff of life" to one-third of the human family, contains eighty per cent. Unripe fruits have much starch in them, which renders them indigestible when eaten uncooked; for the grains of raw starch are but slightly acted upon within the body. But, under the potent chemistry of the sun's ray, this crude material is converted into sugar.

Thus are the fruits prepared by the careful hand of Nature, so that when ripe they may be freely used without further preparation.

[Sidenote: 27. Gum, where found? Its composition? Gum Arabic?]

27. GUM is commonly found in those articles which {62} also contain starch; and has the same chemical composition as the latter, but is much less nutritious. In the East, gum-arabic and similar substances are largely employed as food. Persons who travel by caravan across vast, sandy deserts, find such substances well adapted to their wants, since they are not perishable, and are easily packed and carried.

[Sidenote: 28. The three cla.s.ses of food principles? What besides? What is said of them? Name the articles not nutritious.]

28. STIMULATING SUBSTANCES.--The three cla.s.ses of food-principles already considered--the Alb.u.minoids, the Fats, and the Sugars--comprise all the more important organic ingredients of our food. There are, besides, a great variety of coloring and flavoring matters that stimulate or increase the appet.i.te for food by appealing to the eye and taste; but they are not nutritious, and are quickly separated from the truly useful substances, and do not long remain in the body. Among these may be cla.s.sed spices, flavors of fruits, tea, coffee, and vegetable acids.

[Sidenote: 29. What is said of experiments that have been tried?]

29. NECESSITY OF A REGULATED DIET.--A great variety of experiments have been tried in order to test the relative value of the different nutritive principles. They have been practised to some extent upon man, but chiefly upon those inferior animals which require a similar diet to man.

[Sidenote: 30. What has been demonstrated in the first place? Example?

Second demonstration? Example? Give the ill.u.s.tration in relation to convertibility.]

30. By this means it has been demonstrated that--first, when any one of these substances is eaten exclusively, the body is imperfectly nourished, and life is shortened. Dogs fed exclusively upon either alb.u.men, fat, or sugar, soon die of starvation. Second, a diet long deprived of either of these principles, is a fertile cause of disease; for example, on ship-board, where fresh vegetables are not dealt out for a long period, _scurvy_ becomes prevalent among the sailors. They are, however, to a certain extent mutually convertible, and thus the missing article is indirectly supplied. For {63} instance, sugar changes to fat in the body; and hence, as is well known, the "hands" on a sugar plantation grow fat during the sugar season, by partaking freely of the ripened juices of the cane.

31. That is the best diet therefore which contains some of each of these principles, in due proportion; and that is the worst which excludes the most of them. The cravings and experience of man had unerringly guided him to a correct regulation of his diet, long before the chemistry of food was understood; so that his ordinary meals long ago combined these various principles, the necessity and value of which are now explained.

QUESTIONS FOR TOPICAL REVIEW.

PAGE 1. What is understood by the term food? 53 2. What can you state in relation to the source of food? 53 3. What discriminations and selections are necessary? 53, 54 4. How can you tell the organic from the inorganic substances? 54 5. What relative position does water hold as an article of food? 54 6. In what parts of the body is water found? 54, 55 7. In what articles that we eat is it found? 55 8. If you were required to go without water or solid food for a number of days, which would you prefer to have, and why? 55 9. What can you state of the importance of salt as an article of food? 55, 56 10. How abundant is salt, and how does it find its way into the human system? 55, 56 11. What can you state of the importance of lime in the body? 56 12. What, of the importance of iron? 56, 57 13. What further is stated of other inorganic substances? 57 14. What in relation to organic substances? 57 15. What can you state in relation to the alb.u.minoids? 57, 58 16. What, in relation to alb.u.men? 58 17. What, in relation to casein? 58, 59 18. In relation to the fats or oils, and how generally consumed? 59, 60 19. What do we understand by the sugars or saccharine substances? 60 20. State what you can of sugar--its origin and various qualities. 60, 61 21. Of starch--its varieties and qualities. 61 22. Of the abundance of starch, and its importance as a food principle. 61 23. What is stated in relation to stimulating substances? 62 24. Of the necessity for regulation in diet? 62, 63

{64}

CHAPTER V.

FOOD AND DRINK.

_Necessity for Food--Waste and Repair--Hunger and Thirst--Amount of Food--Renovation of the Body--Mixed Diet--Milk--Eggs--Meat--Cooking--Vegetable Food--Bread--The Potato--Fruits--Purity of Water--Action of Water upon Lead--Coffee, Tea, and Chocolate--Effects of Alcohol._

[Sidenote: 1. What follow activity? Examples? Necessity for food?]

1. NECESSITY FOR FOOD.--Activity is everywhere followed by waste. The engine uses up coal and water to produce motion, the stream wears away its bank, the growing corn-blade draws tribute from the soil. When the human body acts, and it is always in action during life, some of its particles are worn out and thrown off. This waste must constantly be repaired, or the body suffers. In this fact is seen the necessity for food. The particles, thus worn out, being henceforth useless, are removed from the body. Our _food_ and _drink_ are rapidly transformed into a new supply of living, useful material, to be in turn used up and replaced by a fresher supply.

[Sidenote: 2. Give the theory in relation to waste and repair.]