Human Foods and Their Nutritive Value - Harry Snyder (e book reader pc TXT) 📗
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261. Example of a Ration.—Suppose it is desired to calculate a ration for a man at light muscular work. First, note the requirements in the way of nutrients in the table "Dietary Standards," Section 246. Such a ration should supply approximately 0.22 pound each of protein and fat, and 0.77 pound of carbohydrates, and should yield 2800 calories. A trial ration is made by combining the following:
The quantities of nutrients in these food materials are approximately as follows:
It is to be noted that this ration contains approximately the amount of protein called for in the standard ration, while the fat is slightly more and the carbohydrates are less. The food value of the ration is practically that called for in the standard. This ration is sufficiently near the standard to supply the nutrient requirements of a man at light muscular work. To supply palatability, some fruit and vegetables should be added to the ration. These will contribute but little to the nutrient content, but are necessary in order to secure health and the best returns from the other foods, and as previously stated, they are not to be estimated entirely upon the basis of nutrient content. A number of food articles could be substituted in this ration, if desired, either in the interests of economy, palatability, or personal preference.
262. Requisites of a Balanced Ration.—Reasonable combinations of foods should be made to form balanced rations.[2] A number of foods slow of digestion, or which require a large amount of intestinal work, should not be combined; neither should foods which are easily digested and which leave but little indigestible residue. After a ration has been calculated and found to contain the requisite amount of nutrients, it should be critically examined to see whether or not it fulfills the following requirements:
1. Economy and adaptability to the work required.
2. Necessary bulk or volume.
3. Desired physiological influence of the foods upon the digestive tract, whether constipating or laxative in character.
4. Ease of digestion.
5. Effect upon health. It is recognized that there are foods wholesome and nutritious, that cannot be used by some persons, while with others the same foods can be consumed with impunity.
As explained in the chapter on Dietary Studies, the nutrients should be supplied from a number of foods rather than from a few, because it is believed the various nutrients, particularly the proteins, are not absolutely identical from all sources, or equal in nutritive value.
EXAMPLES1. Calculate a ration for a man with little physical exercise.
2. Calculate a ration for a man at hard muscular labor, and give the approximate cost of the ration.
3. Calculate the amounts of food and the nutrient requirements for a family of seven for 10 days; five of the family to consume 0.8 as much as an adult. Calculate the cost of the food; then calculate on the same basis the probable cost of food for one year, adding 20 per cent for fluctuation in market price and additional foods not included in the list.
4. Weigh out the food articles used in problem No. 2, and apportion them among three meals.
CHAPTER XIX WATER263. Importance.—Water is one of the most essential food materials. It enters into the composition of the body, and without it the nutrients of foods would be unavailable, and life could not be sustained. Water unites chemically with various elements to form plant tissue and supplies hydrogen and oxygen for the production of organic compounds within the leaves of plants. In the animal economy it is not definitely known whether or not water furnishes any of the elements of which the tissues are composed, as the food contains liberal amounts of hydrogen and oxygen; it is necessary mainly as the vehicle for distributing nutrients in suspension and solution, and as a medium in which chemical, physical, and physiological changes essential to life processes take place. From a sanitary point of view, the condition of the water supply is of great importance, as impure water seriously affects the health of the consumer.[87]
264. Impurities in Water.—Waters are impure because of: (1) excessive amounts of alkaline salts and other mineral compounds; (2) decaying animal and vegetable matters which act chemically as poisons and irritants, and which may serve as food for the development of objectionable bacterial bodies; and (3) injurious bacteria. The most common forms of impurities are excess of organic matter and bacterial contamination. The sanitary condition of water is greatly influenced by the character of the soil through which it flows and the extent to which it has been polluted by surface drainage.[88]
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
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