The New International Encyclopædia/Sanitary Science

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Edition of 1905. See also Hygiene on Wikipedia, and the disclaimer.

SANITARY SCIENCE. The subdivision of hygiene which treats of ascertained facts and verified theories concerning preservation of health, prevention of disease, and prolongation of life. The subject naturally subdivides into the following principal topics: (1) Those which concern the surroundings of man, such as the site or soil on which his dwelling is placed; the air he breathes; the water he drinks; the character, materials, and arrangements of his dwelling; the cleaning, warming, and ventilation of his dwelling, and the arrangements for the removal from it of excreta; and the general problem of disposal of sewage. (2) The prevention of disease. (3) The personal care of health, covering such points as diet, exercise, and clothing.

Soil. Soils may be moist or dry, permeable or impermeable, flat or sloping, etc. Their characteristics depend, aside from topography, upon the predominance of organic or inorganic constituents, water, and air. Loam contains much organic matter, many earthworms and innumerable bacteria. Deep soil is rarely contaminated with excrementitious matter. At a certain level, dependent upon the position of strata of clay and gravel, is a subterranean collection of water known as ‘ground water.’ It represents the moisture that permeates the surface soil after that is saturated and reaches an impermeable soil upon which it firmly lies, and from whence it is pumped or raised in wells. This subterranean sea is constantly in motion, vertically and horizontally. Its horizontal motion is toward the sea or the nearest watercourse. Its vertical motion is determined chiefly by rainfall. Much importance has been attached to it, and the following points may be considered as accepted: (1) A permanently high ground water, that is, within 5 feet of the surface, is bad, while a permanently low ground water, that is, more than 15 feet from the surface, is good; and (2) violent fluctuations are bad, even with an average low ground water; a comparatively high ground water with moderate and slow fluctuations may be healthful. The ground water determines the spread of certain forms of disease. The rainwater, in the act of passing through the upper strata of earth, carries with it a mass of organic matter as well as a host of bacteria and disease germs, of which it is robbed as it sinks to the deepest soil. If well-water be augmented by ground water which leaches in at high level it will be contaminated and polluted. Healthy soils are the granites, metamorphic rocks, clay slate, limestone, sandstone, chalk, gravel, and sand; unhealthy are clay, sand and gravel with clay subsoil, alluvial soil, and marsh-lands. Among the unhealthy soils ought also to be included all ‘made’ soils, particularly those that are formed so often in towns from rubbish of all sorts. Such soils ought not to be occupied as building sites for at least two years.

Sites. The proper site for a dwelling is upon a permeable, porous soil, through which rain may easily filter and into which it may carry organic matter from the surface; a soil which has a low ground-water level, and which retains but little dampness; a soil which admits of free circulation of atmospheric air with the ground air; a soil that does not admit of collections of standing water, and that has slope enough to insure drainage. Where soil cannot be selected paving and tree-planting correct many evils. Paving prevents the diffusion of ground air and the entrance of sewage or contaminated rainwater. Trees absorb carbonic acid gas and moisture and yield oxygen, which in turn assists chemical conversion of organic matter. Cementing of cellars and laying damp-proof material upon foundations before erecting walls are also protective measures against dampness and pollution. In wet localities or in settlements necessarily built for commercial reasons near marshy land, through subsoil drainage by means of trenches or drain-tile, the level of the ground water may be lowered to a safe position. See Drainage.

Air. Air is an imperfect gas consisting of 79 per cent. of nitrogen and nearly 21 per cent. of oxygen, together with small quantities of carbonic acid, ammonia, watery vapor, and impurities. We may neglect the consideration of the small quantities of helium, neon, argon, krypton, and xenon, the rare gases found in the atmosphere during recent chemical investigations. Air is the prime requisite for existence, and upon its purity depends to a large extent the growth, development, and health of animal life. Saturation of the atmosphere with water is called 100 per cent. of humidity. Average health demands a humidity of from 65 to 75 per cent., the lowest amount of aqueous vapor in the air being 35 per cent. Impurities in the air are from various sources. Air is vitiated by respiration, combustion of fuel or of illuminating gas, decaying vegetable or animal matter, and by gases arising from manufacturing and various occupations. Expired air contains 100 times more carbonic acid and nearly 5 per cent. less oxygen than ordinary atmospheric air. Emitting with each expiration 22 cubic inches of air and respiring 18 times a minute, each adult emits 570,240 cubic inches, or 330 cubic feet of air in 24 hours. In this total there are 14.52 cubic feet of carbon dioxide. Physical activity increases this total. Combustion of fuel and gas adds carbon monoxide and dioxide, smoke, and soot to the atmosphere. Factories, etc., add dust, chemical vapors, and volatile substances to the air. Small amounts of impurity do a little damage to health, large amounts undermine it. Hence ventilation becomes necessary, that is, comparatively pure air must be substituted in dwellings for vitiated atmosphere. See Heating and Ventilation.

Water. The atmosphere is the source of water supply. The vapor of water therein is condensed and falls in the form of rain, snow, or dew. Rain, obviously, must carry down with it the impurities in the atmosphere—gases, dust, and bacteria. It must cause deeper deposition of organic matter as it passes into the soil. It becomes either surface water augmenting the streams, or ground water supplying wells and subterranean reservoirs. Impure water carries the germs of many diseases, as typhoid fever, diphtheria, diarrhoea, dysentery, malaria, cholera, probably yellow fever, etc. The pollution of surface water by the entrance of sewage and of decomposing organic matter is very easy and is a prevalent cause of disease. See Filter and Filtration; also Water Purification; Water Supply; Water-Works.

Dwellings. Besides the site of a dwelling and the desirability of its freedom from dampness and ground air, to which attention has already been given, a house for living or for business purposes should give access to an abundance of sunlight. The heat rays, luminous rays, and actinic rays of light all effect decomposition of organic material and hasten reconstruction processes. The materials of which houses are built are various. Wooden dwellings are common in country localities, but they are always open to the objection of the greater danger of fire. In cities brick or stone is most commonly used, but very good dwellings may be made of concrete. Probably the best material is good, sound, well-burnt brick. Dryness must be secured by means of damp-proof courses along the foundations and hollow walls, and cementing externally. Non-absorbent surfaces internally are important, although some have been inclined to attribute the unhealthfulness of dwellings to the impermeability of the walls obstructing air change. But where air can pass organic matter can lodge and becomes a source of danger. It is better, therefore, to have non-absorbent surfaces as much as possible, and to provide for ventilation in other ways. Paint that can be washed is therefore better than paper. Care should be taken to scrape off all old papers beneath, as they and the paste used with them tend to decompose and become injurious to health. Ceilings ought to be impervious as well as walls, and floors ought to be made of well-fitting seasoned wood, calked and oiled or varnished so as to make them watertight. The proper cubic space has been stated. Arrangements should be made for change of air once in three hours, if conditions of constant change do not exist. The furniture of rooms, especially sleeping rooms, ought not to be too massive; white curtains and hangings too often form traps for dust and organic matter. The warming of houses is of exceeding importance. See Heating and Ventilation.

Scrupulous attention to cleanliness is necessary in dwellings, and there is wisdom in the use of rugs or loose carpets which may be removed daily from rooms and thoroughly cleaned. Corners should be thoroughly freed from dust as well as nooks underneath and behind large pieces of furniture, spaces above rows of books, the wall sides of pictures, etc., for dust forms a well-adapted nidus for disease germs, especially of the bacteria which produce suppuration. Closely allied to the ordinary cleaning of the interior of dwellings is the problem of the removal of excreta, waste, and garbage. Practically waste consists of: (1) Garbage, including kitchen refuse, offal, bones, etc.; (2) refuse, including paper, dust, ashes, clothing, carpet, broken furniture, iron and other waste metal, as well as ‘trade refuse,’ which includes excelsior, straw, wood shavings, leather scraps, tobacco stalks, felt cuttings, tin scraps, etc.; and (3) sewage, including animal excrement (fecal and urinary), wash water from bathing, laundering clothes, washing culinary utensils, cleaning house, etc. Properly separated, ashes and dust are useful in filling sunken lots, marshes, etc. Paper, metal, and most trade refuse have a market value. Sewage and garbage are valuable fertilizers. Yet in most cities all the waste is either burned and destroyed or freighted out and dumped into the sea or some large body of water. It was calculated by a former street-cleaning commissioner in the old city of New York (now the Borough of Manhattan) that the dry refuse reached the aggregate of 1,000,000 tons annually and the garbage 175,000 tons annually. The value of the salvable part of this great mass of waste was stated to be over $650,000 a year. Sanitation is concerned with the disposal of garbage. See Garbage and Refuse Disposal; Sewage Disposal; Plumbing.

Prevention of Disease. This is a large question, on which this article can only briefly touch. Much depends upon knowledge of the ætiology or the remote causes of disease. The best rule for preventing disease is to follow out carefully the principles of general hygiene (q.v.) with reference to pure air, pure water, proper food, cleanliness, etc. Provision may be made against certain diseases. Malaria (q.v.) may be prevented by destroying mosquitoes and depriving them of their breeding places, as well as by screening doors and windows of houses in malarious districts. Smallpox may be prevented by persistent revaccination. (See Vaccination.) Typhoid fever may be prevented by boiling all water before it is drunk or used in cooking, by cooking oysters thoroughly, by most scrupulous drenching of all raw vegetables which may have been watered with liquid manure, and by preventing insects from gaining access to typhoid patient's dejecta or clothing before thorough disinfection has been practiced. (For the diseases transmitted through the agency of insects most of them preventable, see Insects, Propagation of Disease by.) In most large cities compulsory notification to the Board of Health is legal in the case of cholera, yellow fever, plague, smallpox, chicken-pox, diphtheria (including membranous croup), typhus, typhoid, tuberculosis, measles, and spotted, relapsing, and scarlet fevers, all of which are considered contagious except typhoid. Isolation is practiced in all these diseases, partial or absolute. Much stress has been laid upon disinfection as a means of preventing disease, and if properly carried out it has some efficiency. But it is a mistake to place too implicit reliance upon it as ordinarily practiced. See Disinfectants.

The Disposal of the Dead. In order to understand the importance of this subject one must know something of the changes which the body undergoes after death. A body that has been buried gradually breaks up into a large number of comparatively simple compounds, such as carbonic acid, ammonia, sulphureted and carbureted hydrogen, nitrous and nitric acid, and certain more complicated gaseous matters with a very fetid odor, which finally undergo oxidation; while the non-volatile substances usually enter into the soil, and either pass into plants or are carried away by the water percolating the soil. These changes are accelerated by the worms and other low forms of life that usually swarm in decomposing bodies; and the character of the soil materially influences the degree of rapidity of destruction. The bones remain almost unchanged for ages. If a body is burned, decomposition is incomparably more rapid, and different volatile combinations may arise, the mineral salts and a little carbon alone remaining. Putting aside the visionary schemes for turning the dead to commercial account, there are three methods of disposing of our dead for consideration, viz. burial in land or in water, or cremation. At present the question is not urgent; but it may become so in a century or two, if the population continues to increase at the present rate. Even in our own time a great change has taken place, and the objectionable habit of interments in and around churches in towns has been abandoned, cemeteries in the country being now commonly employed, except in the ease of country villages. The air over cemeteries is, however, always contaminated, and water percolating through them is unfit for drinking purposes. The evils are lessened by making the grave as deep as possible, and by placing not more than one body in one grave. Plants should be freely introduced into every cemetery, for the absorption of organic matters and of carbonic acid; and the most rapidly growing trees and shrubs should be selected, in preference to the slowly growing cypress and yew. The superficial space which should be allotted to each grave varies in different countries from 30 to 90 feet; the depth should be at least 6 feet. It is required by law that the grave spaces for persons above twelve years of age shall be at least 9 feet by 4, and those for children under twelve years, 6 feet by 3. It is likewise required that not less than 4 feet of earth should be placed over the coffin of an adult, and 3 feet above that of a child. The time which should elapse before a grave is disturbed for a new tenant varies with the soil and the distance of the body from the surface. Under favorable circumstances, a coffin containing an adult will disappear with its contents in about ten years; while in a clayey or peaty soil it will remain a century. It is generally assumed that a period of fourteen years is sufficient for the decay of an adult, but long before this time all will have disappeared but the skeleton. As a matter of expense, too, that of cremation is greater than burial at sea. In burial at sea the body would go at once to support other forms of life more rapidly than in the case of land burial, and without danger of evolution of hurtful products. See Burial; Cremation.

Diet. Although about seventy elementary substances are known to chemists, only a comparatively small number of these take part in the formation of man and other animals; and it is only this small number of constituents which are essential elements of our food. These elements are, in the order of their abundance, oxygen, carbon, hydrogen, nitrogen, calcium, phosphorus, chlorin, fluorin, sulphur, potassium, sodium, magnesia, and iron, with traces of silicon, lithium, and manganese.

Carbon, hydrogen, nitrogen, and oxygen are supplied to the system by the proteid group of alimentary principles (see Diet)—viz. albumen, fibrin, and casein, which occur both in the animal and vegetable kingdoms, and the gluten contained in vegetables. Animal flesh, eggs, milk, corn, and many other vegetable products contain one or more of these principles. The gelatinoid group also introduces the same elements into the system, when such substances as preparations of gelatin, calves' feet, etc., are taken as food. Carbon, hydrogen, and oxygen are abundantly introduced into the system of the carbohydrate group in the form of sugar or starch (which occur in large quantity in the cereal grains, leguminous seeds, roots, tubers, etc., used as food), and also by organic acids (which, as citric, malic, tartaric acid, etc., occur in numerous vegetables employed as food). Carbon, with hydrogen and oxygen, occurs abundantly in the fatty group of alimentary principles, as, for instance, in all the fat, suet, butter, and oil that are eaten; in the oily seeds, as nuts, walnuts, cocoanuts, etc.; and in fatty foods, as liver, brain, etc. Phosphorus is supplied to us by the flesh, blood, and bones used as food, and in the form of various phosphates it is a constituent of many of the vegetables used as food. The system derives its sulphur from the fibrin of flesh, the albumen of eggs, and the casein of milk, from the vegetable fibrin of corn, etc., from the vegetable albumen of turnips, cauliflowers, asparagus, etc., and from the vegetable casein of peas and beans. Most of the culinary vegetables contain it. Chlorine and sodium, in the form of chloride of sodium, are more or less abundantly contained in all varieties of animal food, and are taken separately as common salt. Potassium is a constitutent of both animal and vegetable food; it occurs in considerable quantity in milk, and in the juice that permeates animal flesh; and most inland plants contain it. We derive the calcium of our system from flesh, bones, eggs, milk, etc. (all of which contain salts of lime); most vegetables also contain lime-salts; and another source of our calcium is common water, which usually contains both bicarbonate and sulphate of lime. Magnesium in small quantity is generally found in those foods that contain calcium. Iron is a constituent of blood found in meat; and it occurs in smaller quantity in milk, in the yolk of egg, and in traces in most vegetable foods. Fluorin occurs in minute quantity in the bones and teeth, obtained from the traces of fluorin found in milk, blood, etc.

These simple bodies are not, however, capable of being assimilated and converted into tissue in the animal body; this combination is effected in the vegetable kingdom, and animals modify and convert the complex compounds which they obtain from vegetables. The number of combined elements varies; thus water contains only 2; sugar, starch, fat, and many organic acids contain 3; while casein, fibrin, and albumen, exclusive of the mineral salts in their ash, contain 5.

It would be impossible, and it is quite unnecessary, to mention in this article the different animals and plants that are used as food by different nations. The interested are referred to Reich's Nahrungs- und Genussmittelkunde (1860-61).

Drinks are merely liquid foods. They include: Mucilaginous, farinaceous, or saccharine drinks—as toast-water, barley-water, gruel, etc., which are very slightly nutritive, and differ but little from common water; aromatic or astringent drinks—as tea, coffee, chocolate, and cocoa, the last two of which contain a considerable quantity of oil and starch; acidulous drinks—as lemonade, ginger beer, raspberry-vinegar water; drinks containing gelatin—the broths and soups, which, if properly prepared, should contain all the soluble constitutents of their ingredients; emulsive or milky drinks—as animal milk, the milk of the cocoanut, and almond milk, a drink prepared from sweet almonds (animal milk contains all the essential ingredients of food, the others are slightly nutritive); alcoholic and other intoxicating drinks—including malt liquor or beer in its various forms of ale, stout, and porter; wines; spirits in their various forms of brandy, rum, gin, whisky. Whether alcoholic drinks constitute food is debatable.

Excluding salt, which must be considered as a saline alimentary principle, the most common condiments, such as mustard, capsicum (Cayenne pepper), pepper, the various spices, etc., owe their action to the presence of a volatile oil. Condiments and sauces afford little or no nutrition. They do, however, exert special action on the nervous system to stimulate secretion and also to retard tissue change and waste. Any more than a very moderate use is likely to impair the digestion and nutritive processes. Salt has a special value in promoting diffusion through the animal membranes and in bringing some of the alimentary principles into solution. Its decomposition probably furnishes the hydrochloric acid to the gastric juice. (For a general discussion of the preparation of foods, see Cookery; and in this connection see, also, Adulteration and Food.) Salted meat is, in so far as nutrition is concerned, in much the same state as meat from which good soup has been made. After flesh has been rubbed and sprinkled with dry salt, a brine is formed amounting in bulk to one-third of the fluid contained in the raw flesh. This brine is found to contain a large quantity of albumen, soluble phosphates, lactic acid, potash salts, creatin, and creatinin—substances which are essential to the constitution of the flesh, which therefore loses in nutritive value in proportion to their abstraction. For a discussion of the preservation of food, see Antiseptics; Food; and Food, Preservation of.

The method of refrigeration is, on a small scale, familiar to every one by the use of ice in the ordinary household refrigerator. (See Refrigeration.) The method of drying—evaporation of water by sun heat or in ovens—is largely applied to meats and to fruits and vegetables. Foodstuffs so treated reabsorb moisture and deteriorate after a time. Certain fruits, as raisins, figs, and dates, are very palatable after such treatment. The method of exclusion of air, sometimes called Appert's method, from its inventor (François Appert, q.v.), is applied to every kind of perishable food, and constitutes one of the great industries of the world. It consists in subjecting the article to be preserved to a temperature sufficient to destroy the germs which cause decomposition, and then putting it into tins or jars, which are immediately made air-tight. This principle is applied in the familiar ‘canning’ of vegetables and fruits. Certain special devices of limited application are resorted to, as the exclusion of air by means of oils and fats and varnishes, or a layer of paraffin.

The method of antiseptics finds application chiefly in the use of smoke, sugar, salt, alcohol, vinegar, and saltpetre.

The pecuniary economy of various foods has been the subject of much investigation in Europe and in the United States. Protein is an essential food, since from no other source can the animal obtain nitrogen; it is also much the costliest form of food. The ratios used by Atwater are 5.3 and 1 for the relative cost of protein fats and carbohydrates. It is, therefore, important economically to obtain protein in its cheapest form, and to use no more than is sufficient for the requisite nitrogen and then to use carbohydrates (starches, etc.) in preference to fats for carbon and hydrogen. Oatmeal, beans, potatoes, and wheat flour are among the cheapest foods, considering their nutritive value, as oysters, salmon, and lobsters are among the costliest. See Food.

Exercise. The most important effect of muscular exercise is produced on the lungs, the quantities of inspired air and of exhaled carbonic acid being very much increased. Taking the air inspired in a given time in the horizontal position as unity, a man walking 3 miles per hour inspires 3.22; and if carrying 34 pounds, 3.5; a man walking 4 miles per hour inspires 5; and when walking 6 miles per hour no less than 7. Almost twice as much carbonic acid is exhaled during exercise as during rest. Hence, muscular exercise is necessary for the due removal of the carbon. The effect of exercise on the mind is not clearly determined; great bodily activity is often observed in association with full mental activity; and better intellectual work can be done by one who exercises physically daily. Digestion is improved by exercise. The appetite increases, and nitrogenous substances, fats, and salts, especially phosphates and chlorides, are required in greater quantity than in a state of rest. The change of tissues is increased by exercise, or, in other words, the excretions give off increased quantities of carbon, nitrogen, water, and salts. The muscles require much rest for their reparation after exercise, and they then absorb and retain water, which seems to enter into their composition. So completely is the water retained in the muscles that the urine is not increased for some hours. The old rule, held by trainers, of only allowing the smallest possible quantity of fluid, is wrong. See Exercise; Gymnastics; Physical Training.

Clothing. The object of clothing is to preserve the proper heat of the body by protecting it from both cold and heat, and thus to prevent the injurious action of sudden changes of temperature upon the skin. The most important materials of clothing are cotton, linen, wool, silk, leather, and india-rubber. Cotton, as a material of dress, wears well, does not rapidly absorb water, and conducts heat much less rapidly than linen, but much more rapidly than wool. From the hardness of its fibres, its surface is slightly rough, and occasionally irritates a very delicate skin. Its main advantages are cheapness and durability. In merino it is mixed with wool in various proportions, and this admixture is far preferable to unmixed cotton. Linen is finer in its fibres than cotton, and hence is smoother. It possesses high conducting and bad radiating powers, so that it feels cold to the skin; moreover, it attracts moisture much more than cotton. For these reasons, cottons and thin woolens are much preferred to linen garments in warm climates. Silk forms an excellent underclothing, but, from its expense, it can never come into general use. Wool is superior both to cotton and linen in being a bad conductor of heat, and a great absorber of water, which penetrates into the fibres and distends them (hydroscopic water), and also lies between them (water of interposition). During perspiration, the evaporation from the surface of the body is necessary to reduce the heat which is generated by exercise. When the exercise is concluded, evaporation goes on, and to such an extent as to chill the body. When dry woolen clothing is put on after exertion, the vapor from the surface of the body is condensed on the wool, and gives out again the large amount of heat which had become latent when the water was vaporized. Therefore, a woolen covering, from this cause alone, at once feels warm when used during sweating. In the ease of cotton and linen, the perspiration passes through them, and evaporates from the external surface without condensation; the loss of heat then continues. These facts make it plain why dry woolen clothes are so useful after exertion. In addition to this, the texture of the wool is warmer, from its bad conducting power, and it is less easily penetrated by cold wind. India-rubber clothing must be used with caution. From its being impervious to air, and from its condensing and retaining perspiration, it is decidedly objectionable; while, on the other hand, its protection against rain is a very valuable property.

In relation to protection against heat, we have to consider the color and not the texture of clothing. White is the best color, then gray, yellow, pink, blue, and black.

The shape and weight of all articles of clothing should be such as to allow of the freest action of the limbs, and in no way to interfere by pressure with the processes of respiration, circulation, and digestion.

Personal Cleanliness. Attention to the state of the skin is of great importance in a hygienic point of view. The perspiration and sebaceous matters which are naturally poured out upon the surface of the body, with an intermingling of particles of detached epidermis, fragments of fibres from the dress, dirt, etc., if not removed, gradually form a crust which soon materially interferes with the due excreting action of the skin. There is little doubt that the daily use of the cold sponge-bath, which less than half a century ago was unknown, and is now a matter of necessity with most healthy persons who have the means of using it, has contributed materially to the preservation of health and the prevention of catarrhal attacks.

Consult: Robinson, Sewage Disposal (London, 1882); Richardson, The Field of Disease: A Book of Preventive Medicine (ib., 1883); Waring, How to Drain a House (New York, 1885), and The Disposal of Sewage and the Protection of Streams Used as Sources of Water Supply (Philadelphia, 1886); Plunkett, Women, Plumbers, and Doctors (New York, 1885); Wilson, Handbook of Hygiene and Sanitary Science (Philadelphia, 8th ed., 1892); Roechling, Sewer Gas and Its Influence Upon Health (London, 1898); Reid, Practical Sanitation (ib., 1901); Baker, Municipal Engineering and Sanitation (New York, 1902); Sedgwick, Principles of Sanitary Science and the Public Health (ib., 1902); Chapin, Municipal Sanitation in the United States.