General Science Part 5

63. The Proteids. The proteids are the building foods, furnishing muscle, bone, skin cells, etc., and supplying blood and other bodily fluids. The best-known proteids are white of egg, curd of milk, and lean of fish and meat; peas and beans have an abundant supply of this substance, and nuts are rich in it. Most of our proteids are of animal origin, but some protein material is also found in the vegetable world. This cla.s.s of foods contains carbon, oxygen, and hydrogen, and in addition, two substances not found in carbohydrates or fats--namely, sulphur and nitrogen. Proteids always contain nitrogen, and hence they are frequently spoken of as nitrogenous foods. Since the proteids contain all the elements found in the two other cla.s.ses of foods, they are able to contribute, if necessary, to the store of bodily energy; but their main function is upbuilding, and the diet should be chosen so that the proteids do not have a double task.

For an average man four ounces of dry proteid matter daily will suffice to keep the body cells in normal condition.

It has been estimated that 300,000,000 blood cells alone need daily repair or renewal. When we consider that the blood is but one part of the body, and that all organs and fluids have corresponding requirements, we realize how vast is the work to be done by the food which we eat.

64. Mistakes in Buying. The body demands a daily ration of the three cla.s.ses of food stuffs, but it is for us to determine from what meats, vegetables, fruits, cereals, etc., this supply shall be obtained (Figs. 28 and 29).

[Ill.u.s.tration: FIG. 28.--Table of food values.]

[Ill.u.s.tration: FIG. 29.--Diagram showing the difference in the cost of three foods which give about the same amount of nutrition each.]

Generally speaking, meats are the most expensive foods we can purchase, and hence should be bought seldom and in small quant.i.ties.

Their place can be taken by beans, peas, potatoes, etc., and at less than a quarter of the cost. The average American family eats meat three times a day, while the average family of the more conservative and older countries rarely eats meat more than once a day. The following tables indicate the financial loss arising from an unwise selection of foods:--

FOOD CONSUMED--ONE WEEK =========================== ======================================= FAMILY No. 1 FAMILY No. 2 --------------------------- --------------------------------------- 20 loaves of bread $1.00 15 lb. flour, bread 10 to 12 lb. loin steak home made (skim milk used) $.45 or meat of similar cost 2.00 Yeast, shortening, and 20 to 25 lb. rib roast skim milk .10 or similar meat 4.40 10 lb. steak (round, Hamburger 4 lb. high-priced cereal and some loin) 1.50 breakfast food, 20 .80 10 lb. other meats, boiling Cake and pastry purchased 3.00 pieces, rump roast, etc. 1.00 8 lb. b.u.t.ter, 30 2.40 5 lb. cheese, 16 .80 Tea, coffee, spices, etc. .75 5 lb. oatmeal (bulk) .15 Mushrooms .75 5 lb. beans .25 Celery 1.00 Home-made cake and pastry 1.00 Oranges 2.00 6 lb. b.u.t.ter, 30 1.80 Potatoes .25 3 lb. home-made shortening .25 Miscellaneous canned goods 2.00 Tea, coffee, and spices .40 Milk .50 Apples .50 Miscellaneous foods 2.00 Prunes .25 3 doz. eggs .60 Potatoes .25 ------- Milk 1.00 $23.45 Miscellaneous foods 1.00 3 doz. eggs .60 - ----- $ 11.30 ----------------------- ----------------------------------------- --- ----------------------- ----------------------------------------- ---

"The tables show that one family spends over twice as much in the purchase of foods as the other family, and yet the one whose food costs the less actually secures the larger amount of nutritive material and is better fed than the family where more money is expended."--From _Human Foods_, Snyder.

The Source of the Different Foods. All of our food comes from either the plant world or the animal world. Broadly speaking, plants furnish the carbohydrates, that is, starch and sugar; animals furnish the fats and proteids. But although vegetable foods yield carbohydrates mainly, some of them, like beans and peas, contain large quant.i.ties of protein and can be subst.i.tuted for meat without disadvantage to the body.

Other plant products, such as nuts, have fat as their most abundant food const.i.tuent. The peanut, for example, contains 43% of fat, 30% of proteids, and only 17% of carbohydrates; the Brazil nut has 65% of fat, 17% of proteids, and only 9% of carbohydrates. Nuts make a good meat subst.i.tute, and since they contain a fair amount of carbohydrates besides the fats and proteins, they supply all of the essential food const.i.tuents and form a well-balanced food.

CHAPTER VI

WATER

65. Destructive Action of Water. The action of water in stream and sea, in springs and wells, is evident to all; but the activity of ground water--that is, rain water which sinks into the soil and remains there--is little known in general. The real activity of ground water is due to its great solvent power; every time we put sugar into tea or soap into water we are using water as a solvent. When rain falls, it dissolves substances floating in the atmosphere, and when it sinks into the ground and becomes ground water, it dissolves material out of the rock which it encounters (Fig. 30). We know that water contains some mineral matter, because kettles in which water is boiled acquire in a short time a crust or coating on the inside. This crust is due to the acc.u.mulation in the kettle of mineral matter which was in solution in the water, but which was left behind when the water evaporated. (See Section 25.)

[Ill.u.s.tration: FIG. 30.--Showing how caves and holes are formed by the solvent action of water.]

The amount of dissolved mineral matter present in some wells and springs is surprisingly great; the famous springs of Bath, England, contain so much mineral matter in solution, that a column 9 feet in diameter and 140 feet high could be built out of the mineral matter contained in the water consumed yearly by the townspeople.

[Ill.u.s.tration: FIG. 31.--The work of water as a solvent.]

Rocks and minerals are not all equally soluble in water; some are so little soluble that it is years before any change becomes apparent, and the substances are said to be insoluble, yet in reality they are slowly dissolving. Other rocks, like limestone, are so readily soluble in water that from the small pores and cavities eaten out by the water, there may develop in long centuries, caves and caverns (Fig.

30). Most rock, like granite, contains several substances, some of which are readily soluble and others of which are not readily soluble; in such rocks a peculiar appearance is presented, due to the rapid disappearance of the soluble substance, and the persistence of the more resistant substance (Fig. 31).

We see that the solvent power of water is constantly causing changes, dissolving some mineral substances, and leaving others practically untouched; eating out crevices of various shapes and sizes, and by gradual solution through unnumbered years enlarging these crevices into wonderful caves, such as the Mammoth Cave of Kentucky.

66. Constructive Action of Water. Water does not always act as a destructive agent; what it breaks down in one place it builds up in another. It does this by means of precipitation. Water dissolves salt, and also dissolves lead nitrate, but if a salt solution is mixed with a lead nitrate solution, a solid white substance is formed in the water (Fig. 32). This formation of a solid substance from the mingling of two liquids is called precipitation; such a process occurs daily in the rocks beneath the surface of the earth. (See Laboratory Manual.)

[Ill.u.s.tration: FIG. 32.--From the mingling of two liquids a solid is sometimes formed.]

Suppose water from different sources enters a crack in a rock, bringing different substances in solution; then the mingling of the waters may cause precipitation, and the solid thus formed will be deposited in the crack and fill it up. Hence, while ground water tends to make rock porous and weak by dissolving out of it large quant.i.ties of mineral matter, it also tends under other conditions to make it more compact because it deposits in cracks, crevices, and pores the mineral matter precipitated from solution.

These two forces are constantly at work; in some places the destructive action is more prominent, in other places the constructive action; but always the result is to change the character of the original substance. When the mineral matter precipitated from the solutions is deposited in cracks, _veins_ are formed (Fig. 33), which may consist of the ore of different metals, such as gold, silver, copper, lead, etc. Man is almost entirely dependent upon these veins for the supply of metal needed in the various industries, because in the original condition of the rocks, the metallic substances are so scattered that they cannot be profitably extracted.

[Ill.u.s.tration: FIG. 33.--Mineral matter precipitated from solution is deposited in crevices and forms veins.]

Naturally, the veins themselves are not composed of one substance alone, because several different precipitates may be formed. But there is a decided grouping of valuable metals, and these can then be readily separated by means of electricity.

67. Streams. Streams usually carry mud and sand along with them; this is particularly well seen after a storm when rivers and brooks are muddy. The puddles which collect at the foot of a hill after a storm are muddy because of the particles of soil gathered by the water as it runs down the hill. The particles are not dissolved in the water, but are held there in suspension, as we call it technically.

The river made muddy after a storm by suspended particles usually becomes clear and transparent after it has traveled onward for miles, because, as it travels, the particles drop to the bottom and are deposited there. Hence, materials suspended in the water are borne along and deposited at various places (Fig. 34). The amount of deposition by large rivers is so great that in some places channels fill up and must be dredged annually, and vessels are sometimes caught in the deposit and have to be towed away.

Running water in the form of streams and rivers, by carrying sand particles, stones, and rocks from high slopes and depositing them at lower levels, wears away land at one place and builds it up at another, and never ceases in its work of changing the nature of the earth's surface (Fig. 35).

[Ill.u.s.tration: FIG. 34.--Deposit left by running water.]

[Ill.u.s.tration: FIG. 35.--Water by its action constantly changes the character of the land.]

68. Relation of Water to Human Life. Water is one of the most essential of food materials, and whether we drink much or little water, we nevertheless get a great deal of it. The larger part of many of our foods is composed of water; more than half of the weight of the meat we eat is made up of water; and vegetables are often more than nine tenths water. (See Laboratory Manual.) Asparagus and tomatoes have over 90 per cent. of water, and most fruits are more than three fourths water; even bread, which contains as little water as any of our common foods, is about one third water (Fig. 36).

[Ill.u.s.tration: FIG. 36.--Diagram of the composition of a loaf of bread and of a potato: 1. ash; 2, food; 3, water.]

Without water, solid food material, although present in the body, would not be in a condition suitable for bodily use. An abundant supply of water enables the food to be dissolved or suspended in it, and in solution the food material is easily distributed to all parts of the body.

Further, water a.s.sists in the removal of the daily bodily wastes, and thus rids the system of foul and poisonous substances.

The human body itself consists largely of water; indeed, about two thirds of our own weight is water. The constant replenishing of this large quant.i.ty is necessary to life, and a considerable amount of the necessary supply is furnished by foods, particularly the fruits and vegetables.

But while the supply furnished by the daily food is considerable, it is by no means sufficient, and should be supplemented by good drinking water.

69. Water and its Dangers. Our drinking water comes from far and near, and as it moves from place to place, it carries with it in solution or suspension anything which it can find, whether it be animal, vegetable, or mineral matter. The power of water to gather up matter is so great that the average drinking water contains 20 to 90 grains of solid matter per gallon; that is, if a gallon of ordinary drinking water is left to evaporate, a residue of 20 to 90 grains will be left. (See Laboratory Manual.) As water runs down a hill slope (Fig. 37), it carries with it the filth gathered from acres of land; carries with it the refuse of stable, barn, and kitchen; and too often this impure surface water joins the streams which supply our cities.

Lakes and rivers which furnish drinking water should be carefully protected from surface draining; that is, from water which has flowed over the land and has thus acc.u.mulated the waste of pasture and stable and, it may be, of dumping ground.

[Ill.u.s.tration: FIG. 37.--As water flows over the land, it gathers filth and disease germs.]

It is not necessary that water should be absolutely free from all foreign substances in order to be safe for daily use in drinking; a limited amount of mineral matter is not injurious and may sometimes be really beneficial. It is the presence of animal and vegetable matter that causes real danger, and it is known that typhoid fever is due largely to such impurities present in the drinking water.

70. Methods of Purification. Water is improved by any of the following methods:--

(_a_) _Boiling_. The heat of boiling destroys animal and vegetable germs. Hence water that has been boiled a few minutes is safe to use.

This is the most practical method of purification in the home, and is very efficient. The boiled water should be kept in clean, corked bottles; otherwise foreign substances from the atmosphere reenter the water, and the advantage gained from boiling is lost.

(_b_) _Distillation_. By this method pure water is obtained, but this method of purification cannot be used conveniently in the home (Section 25).

(_c_) _Filtration_. In filtration, the water is forced through porcelain or other porous substances which allow the pa.s.sage of water, but which hold back the minute foreign particles suspended in the water. (See Laboratory Manual.) The filters used in ordinary dwellings are of stone, asbestos, or charcoal. They are often valueless, because they soon become choked and cannot be properly cleaned.

The filtration plants owned and operated by large cities are usually safe; there is careful supervision of the filters, and frequent and effective cleanings are made. In many cities the filtration system is so good that private care of the water supply is unnecessary.

71. The Source of Water. In the beginning, the earth was stored with water just as it was with metal, rock, etc. Some of the water gradually took the form of rivers, lakes, streams, and wells, as now, and it is this original supply of water which furnishes us all that we have to-day. We quarry to obtain stone and marble for building, and we fashion the earth's treasures into forms of our own, but we cannot create these things. We bore into the ground and drill wells in order to obtain water from hidden sources; we utilize rapidly flowing streams to drive the wheels of commerce, but the total amount of water remains practically unchanged.

The water which flows on the earth is constantly changing its form; the heat of the sun causes it to evaporate, or to become vapor, and to mingle with the atmosphere. In time, the vapor cools, condenses, and falls as snow or rain; the water which is thus returned to the earth feeds our rivers, lakes, springs, and wells, and these in turn supply water to man. When water falls upon a field, it soaks into the ground, or collects in puddles which slowly evaporate, or it runs off and drains into small streams or into rivers. That which soaks into the ground is the most valuable because it remains on the earth longest and is the purest.

[Ill.u.s.tration: FIG. 38.--How springs are formed. _A_, porous layer; _B_, non-porous layer; _C_, spring.]