Human Foods and Their Nutritive Value Part 16

Often present on surface of unclean vegetables.]

284. Sunlight, Pure Water, and Pure Air as Disinfectants.--The most effectual and valuable disinfectants are sunlight, pure water, and pure air. Many kinds of microorganisms, particularly those that are disease-producing, are destroyed when exposed for a time to sunlight.

The chemical action of the sun's rays is destructive to the organic material which makes up the composition of many of these organisms, while higher forms of organic life are stirred into activity by it. The disinfecting power of sunlight should be made use of to the fullest extent, not only in the house, but plenty of sunlight should also be planned for in constructing barns and other buildings where milk-and meat-producing animals are kept. Pure water is also a disinfectant, but when water becomes polluted it loses this power. Many disease-producing organisms are rendered inactive when placed in pure water. Water contains more dissolved oxygen than air, and apparently a portion of the oxygen in water is in a more active condition than that in air. Pure air, too, is a disinfectant; the ozone and hydrogen peroxide and oxides of nitrogen, which are present in traces, exert a beneficial influence in oxidizing organic matter. Fresh air and sunlight, acting jointly, are nature's most effectual disinfectants. Suns.h.i.+ne, fresh air, and pure water are a health-producing trinity. In discussing the importance of pure air, water, and sunlight, Ellen H. Richards[97] says:

"The country dweller surrounds his house with evergreens or shade trees, the city dweller is surrounded with high brick walls.

Blinds, shades, or thick draperies shut out still more, and prevent the beneficial sunlight from acting its role of germ prevention and germ destruction. Bright-colored carpets and pale-faced children are the opposite results which follow. Sunlight, pure air, and pure water are our common birthright which we often bargain away for so-called comforts."

And Dr. Woods Hutchinson says of sunlight:

"It is a splendid and matchless servant in the promoting of healthfulness of the house, for which no subst.i.tute has yet been discovered. It is the foe alike of bacilli and the blues; the best tonic ever yet invented for the liver and for the scalp, and for everything between, the only real complexion restorer, and the deadliest foe of dirt and disease."

[Ill.u.s.tration: FIG. 68.--DIRT AND MANURE EMBEDDED IN SURFACE OF CELERY.]

285. Utensils for Storage of Food.--In order that dishes and household utensils may be kept in the best sanitary condition, they should be free from seams, cracks, and crevices where dust and dirt particles can find lodgment. From the seams of a milk pail that has not been well washed, decaying milk solids can be removed with the aid of a pin or a toothpick. This material acts as a "starter" or culture when pure, fresh milk is placed in the pail, contaminating it and causing it to become sour. Not only is this true of milk, but also of other foods. Wooden utensils are not satisfactory for the handling, storage, or preparation of foods, as it is difficult to keep wood in a sanitary condition.

Uncleanliness of dishes in which foods are placed is too often caused by the use of foul dishcloths and failure to thoroughly wash and rinse the dishes. It is always well to rinse dishes with scalding water, as colds and skin diseases may be communicated from the edges of drinking gla.s.ses, and from forks and spoons, and, unless the dish towels are kept scrupulously clean, it is more sanitary to drain the dishes than to wipe them.

286. Contamination from Unclean Dishcloths.--When the dishcloth is foul, the fat absorbed by the fibers becomes rancid, the proteids undergo putrefaction changes with formation of ill-smelling gases containing nitrogen, the carbohydrates ferment and are particularly attractive to flies, and all the various disease germs collected on the surface of the dishcloth are, along with the rancid fat and other putrifying materials, distributed over the surface of the dishes with which the cloth comes in contact.

[Ill.u.s.tration: FIG. 69.--CONTAMINATION OF WELL WATER FROM SURFACE DRAINAGE.

(After Farmers' Bulletin, U. S. Dept. Agr.)]

287. Refrigeration.--At a low temperature the insoluble or unorganized ferments become inactive, but the chemical ferments or enzymes are still capable of carrying on fermentation. Thus it is that a food, when placed in a refrigerator or in cold storage, continues to undergo chemical change. An example of such enzymic action is the curing of beef and cheese in cold storage. A small amount of ventilation is required when foods are refrigerated, just sufficient to keep up a slight circulation of air. It seems not to be generally understood that all fermentation changes do not cease when food is placed in refrigerators, and this often leads to neglect in their care. Cleanliness is equally as essential, or more so, in the refrigeration of food as in its handling in other ways. Too often the refrigerator is neglected, milk and other food is spilt, filling the cracks, and slow decomposition sets in. A well-cared-for refrigerator is an important factor in the preservation of food, but when it is neglected, it becomes a source of contamination.

Unclean vegetables and food receptacles, impure ice and foul air, are the most common forms of contamination. The chemical changes which foods undergo during refrigeration are such as result in softening of the tissues.

288. Soil.--The soil about dwellings and places where foods are stored frequently becomes polluted with decaying animal and vegetable matter, and in such soils disease-producing organisms readily find lodgment.

Poorly drained soils containing an excess of vegetable matter furnish a medium in which the tapeworm and the germs of typhoid fever, lockjaw, and various diseases affecting the digestive tract, may propagate. The wind carries the dust particles from these contaminated places into unprotected food, where they cause fermentation changes and the disease germs multiply. In considering the sanitary condition of a locality, the character of the soil is an important factor. Whenever there is reason to suspect that a soil is unsanitary, it should be disinfected with lime or formaldehyde. Soils about dwellings need care and frequent disinfecting to keep them in a sanitary condition, equally as much as do the rooms in the dwellings.[99] In the growing of garden vegetables, frequently large quant.i.ties of fertilizers of unsanitary character are used, and vegetables often retain mechanically on their surfaces particles of these. To this dirt clinging to the vegetables have been traced diseases, as typhoid fever and various digestion disorders.

289. Disposal of Kitchen Refuse.--Refuse, as vegetable parings, bones, and meat sc.r.a.ps, unless they are used for food for animals or collected as garbage, should preferably be burned; then there is no danger of their furnis.h.i.+ng propagating media for disease germs. Garbage cans should be kept clean, and well covered to protect the contents from flies. Where the refuse cannot be burned, it should be composted. For this, a well-drained place should be selected, and the refuse should be kept covered with earth to keep off the flies and absorb the odors that arise from the fermenting material, and to prevent its being carried away by the wind. Lime should be sprinkled about the compost heap, and from time to time it should be drawn away and the place covered with clean earth. It is very unsanitary to throw all of the kitchen refuse in the same place year after year without resorting to any means for keeping the soil in a sanitary condition. Although composting refuse is not as sanitary as burning, it is far more sanitary than neglecting to care for it at all, as is too frequently the case.

Ground polluted with kitchen refuse containing large amounts of fatty material and soap becomes diseased, so that the natural fermentation changes fail to take place, and the soil becomes "sewage sick" and gets in such a condition that vegetation will not grow. Failure to properly dispose of kitchen refuse is frequently the cause of the spread of germ diseases, through the dust and flies that are attracted by the material and carry the germs from the refuse pile to food.

[Ill.u.s.tration: FIG. 70.--PLUMBING OF SINK.

1, 1, house side of trap, filled with water; 2, vent pipe; 3, drain pipe connecting with sewer.]

Where there is no drainage system, disposal of the liquid refuse is a serious problem. Drain basins and cesspools are often resorted to, and these may become additional sources of contamination. As stated in the chapter on well water, direct communication is frequently established between such places and shallow wells. Where the only place for the disposal of waste water is the surface of the ground, it should be thrown some distance from the house and where it will drain from and not toward the well. The land should be well drained and open to the sunlight. Coa.r.s.e sand and lime should be sprinkled over it frequently, and occasionally the soil should be removed and replaced with fresh.

Sunlight, aeration, and disinfection of the soil and good drainage are necessary, in order to keep in a sanitary condition the place where the dish water is thrown.

Poor plumbing is often the cause of contaminated food. The gases which escape from unclean traps may carry with them solid particles of organic matter in various stages of decay. The "house side" of traps always ventilates into the rooms, and hence it is important that they be kept scrupulously clean. Where the drip pipe from the refrigerator drains directly into the sewerage system, there is always danger. Special attention should be given to the care of plumbing near places where foods are stored. Frequently there are leaky joints due to settling of the dwellings or to extreme changes in temperature, and the plumbing should be occasionally inspected by one familiar with the subject.[100]

290. General Considerations.--In order to keep food in the most wholesome condition, special care should be taken that all of its surroundings are sanitary. The air, the dishes in which the food is placed, the refrigerator, cellar or closet where stored, and the other food with which it comes in contact, all influence the wholesomeness or cause contamination. A food may contain sufficient nutrients to give it high value, and yet, on account of products formed during fermentation, be poisonous. Foods are particularly susceptible to putrefaction changes, and chemicals and preservatives added as preventives, with a view of r.e.t.a.r.ding these changes, are objectionable, besides failing to prevent all fermentation from taking place. Intelligent thought should be exercised in the care of food, for the health of the consumer is largely dependent upon the purity and wholesomeness of the food supply.

[Ill.u.s.tration: FIG. 71.--A PETRI DISH, SHOWING COLONIES OF BACTERIA PRODUCED BY ALLOWING A HOUSE FLY TO CRAWL OVER SURFACE.

(From Minnesota Experiment Station Bulletin No. 93.)]

CHAPTER XXI

LABORATORY PRACTICE

Object of Laboratory Practice, Laboratory Note-book, and Suggestions for Laboratory Practice.--The aim of the laboratory practice is to give the students an idea of the composition, uses, and values of food materials, and the part which chemistry takes in sanitation and household affairs; also to enable them by simple tests to detect some of the more common adulterants in foods.

Before performing an experiment, the student is advised to review those topics presented in the text which have a bearing upon the experiment, so that a clear conception may be gained of the relations.h.i.+p between the laboratory work and that of the cla.s.s room. The student should endeavor to cultivate the power of observation and to grasp the principle involved in the work, rather than do it in a merely mechanical and perfunctory way. Neatness is one of the essentials for success in laboratory practice, and too much emphasis cannot be laid upon this requisite to good work. The student should learn to use his time in the laboratory profitably and economically. He should obtain a clear idea of what he is to do, and then do it to the best of his ability. If the experiment is not a success, repeat it. While the work is in progress it should be given undivided attention. Care should be exercised to prevent anything getting into the sinks that will clog the plumbing; soil, matches, broken gla.s.s, and paper should be deposited in the waste jars.

[Ill.u.s.tration: FIG. 72.--APPARATUS USED IN LABORATORY WORK.

See page 301 for names.]

A careful record of the experiments should be kept by each student in a suitable note-book. It is suggested that those students desiring more time in writing out the experiments than the laboratory period affords, take notes as they make the various tests, and then amplify and rearrange them in the evening study time. The final writing up of the notes should, however, be done before the next laboratory period.

Careful attention should be given to the spelling, language, and punctuation, and the note-book should represent the student's individual work. He who attempts to cheat by copying the results of others, only cheats himself. In recording the results of an experiment, the student should state briefly and clearly the following:

1. Number and t.i.tle of experiment.

2. How the experiment is performed.

3. What was observed.

4. What the experiment proves.

[Ill.u.s.tration: FIG. 73.--BALANCE AND WEIGHTS.]

LIST OF APPARATUS USED IN EXPERIMENTS

1 Crucible Tongs 2 Evaporating Dishes 1 Ca.s.serole 6 Beakers 12 Test Tubes 1 Wooden Stand 1 Test Tube Stand 1 Sand Bath 2 Funnels 1 Tripod 1 Stoddart Test Tube Clamp 1 Test Tube Brush 1 Burner and Tubing 2 Stirring Rods 6 Watch Gla.s.ses 2 Erlenmeyer Flasks 1 Package Filter Paper 1 Box Matches 1 Wire Gauze 2 Burettes 1 Porcelain Crucible 1 Aluminum Dish

Directions for Weighing.--Place the dish or material to be weighed in the left-hand pan of the balance. With the forceps lay a weight from the weight box on the right-hand pan. Do not touch the weights with the hands. If the weight selected is too heavy, replace it with a lighter weight. Add weights until the pans are counterpoised; this will be indicated by the needle swinging nearly as many divisions on one side of the scale as on the other. The bra.s.s weights are the gram weights. The other weights are fractions of a gm. The 500, 200, 100 mg. (milligram) weights are recorded as 0.5, 0.2, and 0.1 gm. The 50, 20, and 10 mg.

weights as 0.05, 0.02, and 0.01 gm. If the 10, and 2 gm., and the 200, the 100, and the 50 mg. weights are used, the resulting weight is 12.35 gms. No moist substances should ever come in contact with the scale pans. The weights and forceps should always be replaced in the weight box. Too much care and neatness cannot be exercised in weighing.

[Ill.u.s.tration: FIG. 74.]

[Ill.u.s.tration: FIG. 75.--Pouring Reagent from Bottle.]

Directions for Measuring.--Reagents are measured in graduated cylinders (see Fig. 74). When the directions call for the addition of 5 or 10 cc. of a reagent, unless so directed it is not absolutely necessary to measure the reagent in a measuring cylinder. A large test tube holds about 30 cc. of water. Measure out 5 cc. of water and transfer it to a large test tube. Note its volume. Add approximately 5 cc. of water directly to the test tube. Measure it. Repeat this operation until you can judge with a fair degree of accuracy the part of a test tube filled by 5 cc. In the experiments where a burette is used for measuring reagents, the burette is first filled with the reagent by means of a funnel. The tip of the burette is allowed to fill before the readings are made, which are from the lowest point or meniscus. When reagents are removed from bottles, the stopper should be held between the first and second fingers of the right hand (see Fig. 75). Hold the test tube or receptacle that is to receive the reagent in the left hand.

Pour the liquid slowly until the desired amount is secured. Before inserting the stopper, touch it to the neck of the bottle to catch the few drops on the edge, thus preventing their streaking down the sides of the bottle on to the shelf. Replace the bottle in its proper place.

Every precaution should be taken to prevent contamination of reagents.

[Ill.u.s.tration: FIG. 76.--MICROSCOPE AND ACCESSORIES.

1, eye-piece or ocular; 2, objective; 3, stage; 4, cover gla.s.s; 5, slide; 6, mirror.]

Use of the Microscope.--Special directions in the use of the microscope will be given by the instructor. The object or material to be examined is placed on a microscopical slide. Care should be exercised to secure a representative sample, and to properly distribute the substance on the slide. If a pulverized material is to be examined, use but little and spread it in as thin a layer as possible. If a liquid, one or two drops placed on the slide will suffice. The material on the slide is covered with a cover gla.s.s, before it is placed on the stage of the microscope. In focusing, do not allow the object gla.s.s of the microscope to come in contact with the cover gla.s.s. Focus upward, not downward.

Special care should be exercised in focusing and in handling the eye-piece and objective. A camel's-hair brush, clean dry chamois skin, or clean silk only should be used in polis.h.i.+ng the lenses. Always put the microscope back in its case after using.