Experiment 121. -In a place where there is a good draft so that odors will not penetrate the room, burn in an iron spoon over a Bunsen burner (1) small pieces of meat, (2) a little condensed milk or milk powder, (3) part of an egg, and (4) any other food. Is there a residue left after burning? If so, this is mineral matter.
In Experiments 118-121 we found that our ordinary foods are of three great groups of chemical compounds, carbohydrates (starches and sugars), proteins, and fats oroils. The common foods that consist largely of proteins are lean meat, cheese, eggs, beans, and peas. Those largely composed of carbohydrates are most cereals, vegetables and fruits. The fats are butter, pork, nuts and chocolate. Milk contains all three of these compounds in approximately the proportion needed by the body.
Careful experiment has shown that the average, full-grown Americanneeds each day two to three ounces
A DATE PALM.
of proteins, about four ounces of fats and a pound of carbohydrates. The weight of food eaten, however, is very much greater than this, as all foods are composed largely of water. The proteins are needed for growth and repair, since the living part of the cells, the protoplasm, is composed of proteins. The rest of the food furnishes energy.
Until recently, it was thought that a great deal of meat was necessary to furnish the energy needed for hard muscular work. But nowinvestigation has shown that this energy can better be supplied by other foods and that eating too much meat is not only needlessly expensive but bad for the system. The staple food of northern Africa and southwestern Asia is the date palm, which is admirable for hot climates. In cold regions where the body requires great energy to keep up its heat, much fat is eaten and sugar, if procurable. The exact kind of food used must always depend largely on its availability and on the tastes of the individual, but the diet should be so varied as to contain sufficient of each of the three great classes of foods.
Besides the necessary foods, most individuals desire especial additions for relishes and beverages. These commonly consist of spices, tea and coffee and other like materials. When used in moderation, they are usually a benefit, as they stimulate the appetite. But excessive use is harmful.
Alcohol, except possibly in exceedingly smallquantities, cannot be considered a food, and
A BUNCH OF DATES.
as a stimulator for the appetite it should not be used. Many careful experiments have shown that while it may stimulate the body temporarily, it does not enable it to do more work. Instead, those using it cannot do as much work, or withstand as great physical or mental strain, as those not using it. Even if it were not for the ungovernable appetite which its use almost invariably engenders, and for the degrading influences with which its use is usually surrounded, its physiological action is such as to lessen the body"s vitality, decrease its resistance to disease, and dull its nervous and mental efficiency.
Careful scientific experiments have also been made upon the effect of tobacco. Although there are differences of opinion about its effect upon fully matured adults, there is no such difference of opinion in regard to its effect upon those who have not stopped growing and are not yet fully matured. Measurements and comparisons made in regard to the physical development, endurance and mental ability of a largenumber of college men has shown conclusively that those who have not used tobacco, as a rule, have better physiques, are better students and can stand more physical exercise than those who have used it. In the competition for athletic teams it is found that only about half as many of those who have used tobacco make good, as of those who have not used it.
COFFEE PLANT.
Showing the clusters of beans from which coffee is produced.
111.Preparation of Foods. -When foods are appetizing, look good, smell good and taste good, both the saliva and the gastric juice are secreted in larger quantities, so that this sort of food, when taken into the system, is more readily digested than food which is not attrac- tive. One of the reasons for cooking food is to render it appetizing, and this should never be lost sight of by the cook. Cooking also softens and loosens the fibers of meats and causes the cell walls of the starch gran- ules to burst, thus rendering it possible for the digestive juices to attack the food more readily. In addition, cooking kills the germs and other parasites that are sometimes found in foods.
To cook food properly is a fine art and requires most careful studyand great skill. The science of providing economically the kinds offood necessary and of cooking these properly so that they will be attractive, easily digested and will lose none of their nutritive value, is one that is at present in its infancy. Human beings, like other animals, must have a balanced ration or diet if they are to be most productive economically. They differ from other animals in having a much greater range of food possibilities and in being much more sensitive as to the appearance and taste of food.
Summary. -Plants and animals form the live part of the earth. Most plants consist of root, stem and leaves. The root takes in all the plant"s food except carbon and oxygen. These are supplied through the leaves. The leaves are the original food manufactories for all plants and animals. They are supported on the stem, of which there are two great classes, monocotyledonous and dicotyledonous.
The stems also support the flower, which usually consists of calyx,corolla, stamen and pistils. The chief function of the flower is to produce the seeds by which the plants are reproduced. The pollen grains which are necessary for the fertilization of the egg cells are carried and spread by the wind and by insects and birds. The seeds are also scattered by the wind and by animals and sometimes by floating down streams.