Human Foods and Their Nutritive Value

Fig. 61.—Dirt and Impurities in a Surface Well Water.

265. Mineral Impurities.—- The mineral impurities of water are mainly soluble alkaline and similar compounds dissolved by the water in passing through various layers of soil and rock. When water contains a large amount of sodium chloride, sodium sulphate or carbonate, or other alkaline salts, it is termed an "alkali water." Where water passes through soil that has been largely formed from the decay of rocks containing alkaline minerals, the water dissolves some of these minerals and becomes alkaline. The kind of alkali determines the character of the water; in some cases it is sodium carbonate, which is particularly objectionable. The continued use of strong alkali water causes digestion disorders, because of the irritating action upon the digestive tract. Hard waters are due to the presence of lime compounds. In regions where limestone predominates, the carbon dioxid in water acts as a solvent, producing hard waters. Waters that are hard on account of the presence of calcium carbonate give a deposit when boiled, due to liberation of the carbon dioxid which is the material that renders the lime soluble. Calcium sulphate, or gypsum, on the other hand, imparts permanent hardness. There is no deposit when such waters are boiled. A large number of minerals are found in various waters, often sufficient in amount to impart physiological properties. Water that is highly charged with mineral matter is difficult to improve sufficiently for household purposes. About the only way is by distillation.^[89]

266. Organic Impurities.—Water that flows over the surface of the ground comes in contact with animal and vegetable material in various stages of decay, and as a result some is dissolved and some is mechanically carried along by the water. After becoming soluble, the organic matter undergoes further chemical changes, as oxidation and nitrification caused by bacteria. If the organic matter contain a large amount of nitrogenous material, particularly of proteid origin, a series of chemical changes induced by bacterial action takes place, resulting in the production of nitrites. The nitrifying organisms first produce nitrous acid products (nitrites), and in the further development of the nitrifying process these are changed to nitrates. The ammonia formed as the result of the decomposition of nitrogenous organic matter readily undergoes nitrification changes. Nitrates and nitrites alone are not injurious in water, but they are usually associated with objectionable bacteria and generally indicate previous contamination.^[90]

267. Interpretation of a Water Analysis.—"Total solid matter" represents all the mineral, vegetable, and animal matter which a water contains. It is the residue obtained by evaporating the water to dryness at a temperature of 212° F. Average drinking water contains from 20 to 90 grains per gallon of solid matter. "Free ammonia" is that formed as a result of the decomposition of animal or vegetable matter containing nitrogen. Water of high purity usually contains less than 0.07 parts per million of free ammonia. "Albuminoid ammonia" is derived from the partially decomposed animal or vegetable material in water. The greater the amount of nitrogenous organic impurities, the higher the albuminoid ammonia. A good drinking water ought not to contain more than 0.10 part per million of albuminoid ammonia. An abnormal quantity of chlorine indicates surface drainage or sewage contamination, or an excess of alkaline matter, as common salt. Nitrites should not be present, as they are generally associated with matter not completely oxidized. Nitrites are usually considered more objectionable than nitrates; both are innocuous unless associated with disease-producing nitroörganisms.

268. Natural Purification of Water.—River waters are sometimes dark colored because of large amounts of dissolved organic matter, but in contact with the sun and air they gradually undergo natural purification and the organic matter is oxidized. However, absolute reliance cannot be placed upon natural purification of a bad water, as the objectionable organisms often have great resistive power. There is no perfectly pure water except that prepared in the chemical laboratory by distillation. All natural waters come in contact with the soil and air, and necessarily contain impurities proportional to the extent of their contamination.

269. Water in Relation to Health.—There are many diseases, of which typhoid fever is a type, that are distinctly water-born. The typhoid bacilli, present in countless numbers in the feces of persons suffering or convalescent from typhoid fever, find their way into streams, lakes, and wells.^[91] They retain their vitality, and when they enter the digestive tract of an individual, rapidly increase in numbers. Numerous disastrous outbreaks of typhoid fever have been traced to contamination of water. Coupled with the sanitary improvement of a city's water supply, there is diminution of typhoid fever cases, and a noticeable lowering of the death rate. Many cities and villages are dependent for their water upon rivers and lakes into which surface drainage finds its way, with all contaminating substances. Mechanical sedimentation and filtration greatly improve waters of this class, but do not necessarily render them entirely pure. Compounds of iron and aluminium are sometimes added in small amounts, under chemical supervision, to such waters to precipitate the organic impurities. Spring waters are not entirely above suspicion, as oftentimes the soil through which they flow is highly polluted. All water of doubtful purity should be boiled, and there are but few natural waters of undoubted purity. There is no such thing as absolutely pure water in a state of nature. The mountain streams perhaps approach nearest to it where there are no humans to pollute the banks; but then there are always the beasts and birds, and they, too, are subject to disease. There are very few waters that at some time of the year and under some conditions are not contaminated with disease-producing organisms. No matter how carefully guarded are the banks of lakes furnishing the water supply of cities, more or less objectionable matter will get in. In seasons of heavy rains, large amounts of surface water enter the lakes, carrying along the filth gathered from many acres of land drained by the streams entering the lakes. Some of the most serious outbreaks of typhoid fever have come from temporary contamination of ordinarily fairly good drinking water. In general, too little attention is given to the purity of drinking water. It is just as important that water should be boiled as that food should be cooked. One of the objects of cooking is to destroy the injurious bacteria, and they are frequently more numerous in the drinking water than in the food.

The argument is sometimes advanced that the mineral matter present in water is needed for the construction of the bone and other tissues of the body, and that distilled water fails to supply the necessary mineral matter. This is an erroneous assumption, as the mineral matter in the food is more than sufficient for this purpose. When water is highly charged with mineral salts, additional work for their elimination is called for on the part of the organs of excretion, particularly the kidneys; and furthermore, water nearly saturated with minerals cannot exert its full solvent action.

In discussing the immediate benefits resulting from improvement of water, Fuertes says:^[92]

There is a very close relationship between the surface water and that of shallow wells. A shallow well is simply a reservoir for surface water accumulations. It is stated that, when an improved system of drainage was introduced into a part of London, many of the shallow wells became dry, indicating the source from which they received their supply. Direct subterranean connection between cesspools and wells is often traced in the following way: A small amount of lithium, which gives a distinct flame reaction, and a minute trace of which can be detected with the spectroscope, is placed in the cesspool, and after a short time a lithium reaction is secured from the well water.

Rain water is relied upon in some localities for drinking purposes. That collected in cities and in the vicinity of barns and dwellings contains appreciable amounts of organic impurities. The brown color is due to the impurities, ammonium carbonate being one of these. There are also traces of nitrates and nitrites obtained from the air. When used for drinking, rain water should be boiled.

270. Improvement of Waters.—Waters are improved by: (1) boiling, which destroys the disease-producing organisms; (2) filtration, which removes the materials mechanically suspended in the water; and (3) distillation, which eliminates the impurities in suspension and solution, as well as destroys all germ life.

271. Boiling Water.—In order to destroy the bacteria that may be in drinking water, it is not sufficient to heat the water or merely let it come to a boil. It has been found that if water is only partially sterilized and then cooled in the open air, the bacteria develop more rapidly than if the water had not been heated at all. It should boil vigorously five to ten minutes; cholera and typhoid bacteria succumb in five minutes or less. Care should be taken in cooling that the water is not exposed to dust particles from the air nor placed in open vessels in a dirty refrigerator. It should be kept in perfectly clean, tight-stoppered bottles. These bottles should be frequently scalded. Great reliance may be placed upon this method of water purification when properly carried out.

272. Filtration.—Among the most efficient forms of water filters are the Berkefeld and Pasteur. The Pasteur filter is made of unglazed porcelain, and the Berkefeld of fine infusorial earth (finely divided SiO₂). Both are porous and allow a moderately rapid flow of water. The flow from the Berkefeld filter is more rapid than from the Pasteur. The mechanical impurities of the water are deposited upon the filtering surface, due to the attraction which the material has for particles in suspension. These particles usually are the sources of contamination and carry bacteria. When first used, filters are satisfactory, but unless carefully looked after they soon lose their ability to remove germs from the water and may increase the impurity by accumulation. Small faucet filters are made of porous stone, asbestos, charcoal, etc. Many of them are of no value whatever or are even worse than valueless. Filters should be frequently cleansed in boiling water or in steam under pressure. Unless this is done, the filters may become incubators for bacteria.

273. Distillation.—When an unquestionably pure water supply is desired, distillation should be resorted to. There are many forms of stills for domestic use which are easily manipulated and produce distilled water economically.^[93] The mineral matter of water is in no way essential for any functional purpose, and hence its removal through distillation is not detrimental.

Fig. 63.—Water Still.

274. Chemical Purification.—Purification of water by the use of chemicals should not be attempted in the household or by inexperienced persons. When done under supervision of a chemist or bacteriologist, it may be of great value to a community. Turneaure and Russell,^[94] in discussing the purification of water by addition of chemicals, state:

275. Ice.—The purity of the ice supply is also of much importance. While freezing reduces the number of organisms and lessens their vitality, it does not make an impure water absolutely wholesome. The way, too, in which ice is often handled and stored subjects it to contamination, and foods which are placed in direct contact with it mechanically absorb the impurities which it contains. For cooling water, ice should be placed around rather than in it. Diseases have frequently been traced to impure ice. The only absolutely pure ice is that made from distilled water.

276. Mineral Waters.—When water is charged with carbonic acid gas under pressure, carbonated water results, and when minerals, as salts of sodium, potassium, or lithium, are added, artificial mineral waters are produced. Natural mineral waters are placed on the market to some extent, but most mineral waters are artificial products and they are sometimes prepared from water of low sanitary character. Mineral waters should not be used extensively except under medical direction, as many have pronounced medicinal properties. Some of the constituents are bicarbonates of sodium, potassium, and lithium; sulphates of magnesium (Epsom salts) and calcium; and chloride of sodium. The sweetened mineral waters, as lemonade, orangeade, ginger ale, and beer, contain sugar and organic acids, as citric and tartaric, and are flavored with natural or artificial products. Most of them are prepared without either fruit or ginger. Natural mineral waters used under the direction of a physician are often beneficial in cases of chronic digestion disorders or other diseases.

277. Materials for Softening Water.—The materials most commonly used for softening water are sodium carbonate (washing soda), borax, ammonia, ammonium carbonate, potash, and soda lye. Waters that are very hard with limestone should have a small amount of washing soda added to them. Two ounces for a large tub of water is the most that should be used, and it should first be dissolved in a little water. If too much soda is used, it is injurious, as only a certain amount can be utilized for softening the water, and the excess simply injures the hands and fabric. When hard limewater is boiled and a very little soda lye added, a precipitate of carbonate of lime is formed, and then if the water is strained, it is greatly improved for washing purposes. Borax is valuable for making some hard waters soft. It is not as strong in its action as is sodium carbonate. For the hardest water ¼ pound of borax to a large tubful may be used; most waters, however, do not need so much. Ammonia is one of the most useful reagents for softening water. It is better than washing soda and borax, because the ammonia is volatile and does not leave any residue to act on the clothes, thus causing injury. For bathing purposes, the water should be softened with ammonia, in preference to any other material. Ammonia should not be poured directly into hot water; it should be added to the water while cold, or to a small quantity of cold water, and then to the warm water, as this prevents the ammonia from vaporizing too readily. Ammonia produces the same effect as potash or soda lye, without leaving a residue in the garments washed. It is especially valuable in washing woolen goods or materials liable to shrink. Waters which are hard with alum salts are greatly benefited by the addition of ammonia. A little in such a water will cause a precipitate to form, and when the water is strained it is in good condition for cleaning purposes. Ammonium carbonate is used to some extent as a softening and cleaning agent, and is valuable, as there is no injurious effect upon clothing, because it readily volatilizes. Caustic potash and caustic soda are sometimes employed for softening water, but they are very active and are not adapted to washing colored or delicate fabrics. They may be used for very heavy and coarse articles that are greasy,—not more than a gram in a gallon of water. Bleaching powder is not generally a safe material for cleansing purposes, as it weakens the texture of clothing. After a contagious disease, articles may be soaked in water containing a little bleaching powder and a few drops of carbolic acid, followed by thorough rinsing and bleaching in the sun. But as a rule formaline is preferable for disinfecting clothing. It can be used at the rate of about one pound to 100 gallons of water. Bleaching powder, caustic potash or soda, and strong soap are not suitable for cleaning woodwork, because of the action of the alkali on paint and wood; they roughen the surface and discolor the paint. Waters vary so in composition, that a material suitable for softening one may not prove to be the best for softening another. The special kind must be determined largely by trial, and it should be the aim to use as little as possible. When carbolic acid, formaline, bleaching powder, and caustic soda are used, the hands should be protected and the clothes should be well rinsed.

278. Economic Value of a Pure Water Supply.—From a financial point of view, the money spent in securing pure water is one of the best investments a community can make. Statisticians estimate the death of an adult results in a loss to the state of from $1000 to $5000; and to the losses sustained by death must be added those incurred by sickness and by lessened quality and quantity of work through impaired vitality,—all caused by using poor drinking water. Wherever plants have been installed for improving the sanitary condition of the water supply, the death rate has been lowered and the returns to the community have been far greater than the cost of the plant. Impure water is the most expensive food that can be consumed.

CHAPTER XX

279. Injurious Compounds in Foods.—An ordinary chemical analysis of a food determines only the nutrients, as protein, carbohydrates, and fats; and unless there is reason to believe the food contains injurious substances no special tests for these are made. There are a number of poisonous compounds that foods may contain, and many of them can but imperfectly be determined by chemical analysis. Numerous organic compounds are produced in foods as the result of the workings of microörganisms; some of these are poisonous, while others impart only special characteristics, as taste and odor. The poisonous bacteria finding their way into food produce organic compounds of a toxic character; and hence it is that the sanitary condition of a food, as influenced by preparation and storage, is often of more vital importance than the nutrient content.^[95]

280. Sources of Contamination of Food.—As a rule, too little attention is given to the sanitary handling and preparation of foods. They are often exposed to impure air and to the dust and filth from unclean streets and surroundings, and as a result they become inoculated with bacteria, which are often the disease-producing kind. Gelatine plates exposed by bacteriologists under the same conditions as foods develop large numbers of injurious microörganisms. In order to avoid contamination in the handling of food, there must be: (1) protection from impure air and dust; (2) storage in clean, sanitary, and ventilated storerooms and warehouses; (3) storage of perishable foods at a low temperature so as to retard fermentation changes; and (4) workmen free from contagious diseases in all occupations pertaining to the preparation of foods. Ordinarily, foods should not be stored in the paper wrappers in which they are purchased, as unclean paper is often a source of contamination.

281. Sanitary Inspection of Food.—During recent years some state and city boards of health have introduced sanitary inspection of foods, with a view of preventing contamination during manufacture and transportation, and this has done much to improve the quality and wholesomeness. Putrid meats, fish, and vegetables are not allowed to be sold, and foods are required to be handled and stored in a sanitary way. Next to a pure water supply, there is no factor that so greatly influences for good the health of a community as the sanitary condition of the food. While the cooking of foods destroys many organisms, it often fails to render innocuous the poisons which they produce, and furthermore the unsound foods when cooked are not entirely wholesome, and they have poor keeping qualities.

Often meats, vegetables, and other foods eaten uncooked, as well as the numerous cooked foods, are exposed in dirty market places, and accumulate large amounts of filth, and are inoculated with disease germs by flies. Protection of food from flies is a matter of vital importance, as they are carriers of many diseases. In the case of typhoid fever, next to impure drinking water flies are credited with being the greatest distributors of the disease germs.^[96]

Fig. 66.—Diphtheria Bacilli. (After Conn.)

Often present in dust particles and in food unprotected from dust.

282. Infection from Impure Air.—The dust particles of the air contain decayed animal and vegetable matter in which bacteria are present; these find their way into the food when it is not carefully protected, into the water supply, and also into the lungs and other organs of the body. When foods are protected from the mechanical impurities which gain access through the air, and fermentation is delayed by storage at a low temperature, digestion disorders are greatly lessened. From a sanitary point of view, the air of food storerooms and of living rooms should be of equally high purity. When foods are kept in unventilated living rooms, they become contaminated with the impurities thrown off from the lungs in respiration, which include not only carbon dioxid, but the more objectionable toxic organic materials.

Vegetable foods need to be stored in well-ventilated places, as the plant cells are still alive and carrying on life functions, as the giving off of carbon dioxid, which is akin to animal respiration; in fact, it is plant-cell respiration. Provision should be made for the removal of the carbon dioxid and other products, as they contaminate the air. When vegetable tissue ceases to produce carbon dioxid, death and decay set in, accompanied by fermentation changes.

283. Storage of Food in Cellars.—Cellars are often in a very unsanitary condition, damp, poorly lighted, unventilated, and the air filled with floating particles from decaying vegetables. The walls and shelves absorb the dust and germs from the foul air and are bacterially contaminated, and whenever a sound food is stored in such a cellar, it readily becomes inoculated with bacteria. There is a much closer relationship existing between the atmosphere of the cellar and that of the house than is generally realized. An unclean cellar means contaminated air throughout the house. When careful attention is given to the sanitary condition of the cellar, many of the more common diseases are greatly reduced. Cases of rheumatism have often been traced to a damp cellar. In some localities where the cellars are unusually unsanitary, there is in the season of spring rains, when they are especially damp and contain the maximum of decayed vegetation, a prevalence of what might be called "cellaritis." The symptoms differ and the trouble is variously attributed, but the real cause is the same, although overlooked, for, unfortunately, doctors do not visit the cellar.

Cellars should be frequently cleaned and disinfected, using for the purpose some of the well-known disinfectants, as formaline, bleaching powder, or a dilute solution of carbolic acid. It has been found in large cities, when the spread of such diseases as yellow fever was imminent, that a general and thorough cleaning up of streets and cellars with the improved sanitary conditions resulting greatly lowered the usual death rate.

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 microörganisms, 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. Sunshine, 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:

And Dr. Woods Hutchinson says of sunlight:

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 glasses, 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.

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 quantities 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 scraps, unless they are used for food for animals or collected as garbage, should preferably be burned; then there is no danger of their furnishing 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.

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. Coarse sand and lime should be sprinkled over it frequently, and occasionally the soil should be removed and replaced with fresh. Sunlight, aëration, 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 retarding 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.

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

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 title of experiment.
• 2. How the experiment is performed.
• 3. What was observed.
• 4. What the experiment proves.

List of Apparatus used in Experiments

• 1 Crucible Tongs
• 2 Evaporating Dishes
• 1 Casserole
• 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 Glasses
• 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 brass 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.