is not warm enough for a healthy person, we may be sure that it is because the humidity is too low. The problem of constructing buildings in such a way as to keep the interior up to a fair degree of humidity is a large one. So far engineers have made little practical progress toward its solution. Satisfactory devices may be had to improve the moisture in large public buildings, but these devices have so far proved too expensive for private dwellings, offices, or schoolrooms. The humidity in living rooms may be improved by setting about growing plants and porous dishes, such as flower pots full of water. If such receptacles are set near electric fans evaporation is facilitated. Pans or pots of water may also be placed upon the radiator. CHAPTER III MISCELLANEOUS Odors. Odors in a living room come mostly from human sources. The sources of these odors are: foul breath, decaying teeth, unclean mouths, nasal catarrh, sudoriferous glands, especially those of the pubes, feet, and axillæ, also gases from the stomach and bowels. The decomposition of matter on the skin and also in the clothes adds a very disagreeable odor, accentuated in a warm moist atmosphere. The peculiar odor in some rooms, especially sick rooms, seems to be none of these; just what constitutes the somewhat characteristic man-smell is not known. While odors may be very unpleasant, they are not known to seriously influence health; contrary to common opinion, they are not by any means a reliable sign of danger. The presence of bacteria or dust in the atmosphere has no special relation to odors. Some poisonous gases, such as carbon monoxid, are practically inodorous. The air of inhabited rooms ordinarily must be quite full of various scents which we do not appreciate, either because our sense of smell is not keen enough, or because we have become so accustomed to them that they are not noticed. An atmosphere that does not appear to be unpleasant while remaining in a room may seem intolerable upon returning to it after a period in the fresh outdoor air. Man's sense of smell is not keen when compared to that of some of the lower animals; nevertheless it is extremely sensitive to certain odors. Thus, it can determine 0.000,000,03 gram of musk. The acuteness of the sense of smell varies markedly in different individuals. When a room smells stuffy and close it may be taken as a fairly reliable index that the air is vitiated; this is especially true in a clean room not complicated with odors from clothing and sources other than man. In fact, the odors observed upon entering a room from the outside fresh air often furnish better evidence of imperfect ventilation than laboratory tests. De Chaumont made accurate observations and found that when the CO2 amounts to 6 parts per 10,000 the atmosphere begins to smell 2 close and stuffy. Pettenkoffer found air containing 7.5 parts of CO. per 10,000 from the expired breath to have a marked odor, and 10 parts a very unpleasant odor. With a little practice various grades of vitiated air can be detected up to 10 or 12 parts of CO2 per 10,000. The odors from marshes and from decomposing organic matter are not apparently hurtful. One of the most famous stenches that has been recorded, if not the most famous, was that which arose in 1858 and 1859 from the Thames, which at that time was grossly polluted with the sewage of London (Sedgwick). Dr. Budd insisted that no very serious results followed. After giving his proof Budd1 states: "Before these inexorable figures the illusions of half a century vanished in a moment." We now know that odors in the air bear no reference to contagion or infection and, however unpleasant, need not be feared as such. Sewer "gas" is discussed on page 638. The effect of odors upon health is not at all understood. When we sense a pleasant smell we involuntarily take deeper breaths; on the other hand, unpleasant odors diminish the respiratory exchange. The latter are accordingly harmful to that extent and the former stimulat ing. Odors influence the nervous system in various ways; some stimulate, others depress psychic activity; some odors have a well-known influence upon sexuality. Occasionally odors are so disagreeable that they induce nausea, even vomiting. It is remarkable how quickly we may become accustomed to odors, but because our sense of smell has been dulled is no guarantee that the cause of the odors may not continue to produce its effects. Leonard Hill thinks that it is very doubtful if the unpleasant smelling exhalations of the bodies of men have any ill effects on men accustomed to them, and not of esthetic temperament. Light. All the rays of the sun pass through the atmosphere before they reach the earth. The air acts as a differential filter, holding back many rays, especially those of shorter wave-length; that is, the ultraviolet end of the spectrum. These rays have marked chemical power. Bunsen and Roscoe investigated this question of the atmospheric absorp tion of the chemical rays of the sun, and came to the conclusion that in passing through the atmosphere the ultraviolet rays lost about 66 per cent. of their chemical power. We have already seen that many of the heat rays are also absorbed by the atmosphere. "More heat and we might be roasted, more light and we might be 'Dr. William Budd: "Typhoid Fever: Prevention," pp. 148-151. London, 1873. which the student is advised to read. Its Nature, Mode of Spreading, and The waves of light are not waves of the atmosphere, but of the ether; how ever, they are absorbed, reflected or refracted by the dust and moisture contained in the air. It is convenient to consider light, as well as electricity and radioactivity, at this point. blinded, more chemical energy and we might be slain like the microbes. The rays of shorter wave-lengths have chemical and photodynamic powers which must have an important relation to health. These rays act upon photographic negatives; hasten the hatching of flies' eggs and frogs' eggs; they sunburn the skin; they kill many bacteria, including the tubercle bacilli; they cause heliotropism; they combine chlorin and hydrogen into hydrochloric acid; they cause the oxidation of oxalic acid and other chemical reactions; they blacken silver salts. It has been shown that in buckwheat poisoning (fagotoxismus) these actinic rays play an important part. The skin eruptions upon the exposed surfaces in pellagra are also explained upon the photodynamic theory, that is, the poison is believed to be activated by certain light rays. The air as a filter of the sun's rays bears a very important but little understood relation to life. It is now well known that some of the sun's rays have intense chemical and "vital" power. We know something about the chemical rays, the luminous rays, and the calorific rays, but there are doubtless many ether vibrations of which we know nothing. Macfie speculates that, "even, indeed, as the crops of the northern zone outstrip the crops in the south of France, so at certain times may the activity of nations be stimulated or depressed by atmospheric variations affecting the composition of solar radiation.” The physiological action of light is just beginning to receive the serious attention it deserves. We are all familiar with the calming effect of the dim religious light of churches and the stimulating effect of the glare of the theater. The intense light of the tropics and of high altitudes is believed in some way to bring on nervous disorders, but the relation is but vaguely understood. Some of the ill effects of rooms, attributed to bad air and poor ventilation, are due in part to the over-stimulation of excessive illumination. METHOD FOR MEASURING ILLUMINATION.-The method which is recommended as a standard procedure depends on the use of photosensitive paper, such as can be obtained from any dealer in photographic materials. By exposing the sensitized paper through a slot in a cardboard for a sufficient period of time, and noting the number of seconds or minutes consumed to match in depth a standard shade of color, the intensity of light can be determined with accuracy. If a fresh piece of paper is exposed to the direct rays of the sun for three seconds it will assume a shade which can be used as a standard for a given series of tests. The intensity of light at other points may be compared with this by noting the number of seconds required to color a fresh piece of paper from the same lot to the same shade. Electricity. The question of electricity is also a question of vibra tions, not of the air, but of ether, and one shrouded in much obscurity. The electric potential of the air varies considerably. It is highest in winter and lowest in summer, and shows diurnal variations. It is increased by winds and is especially increased by the condensation of vapor. It also increases as we ascend. It is assumed that electric changes in the air and in other objects surrounding us exercise an influence on health and vitality, but the influence is obscure and mainly a matter of conjecture. Radioactivity. Soon after the discovery of radium by the Curies it was proved, chiefly through the investigations of Elster and Geitel, that the air and soil and certain mineral springs contained radioactive substances. Newly fallen rain and snow are also radioactive. Air drawn from the soil by means of a pipe, or air shut up in underground cellars and caverns, is specially radioactive, as is also the air on mountain tops. The air in clear weather has greater radioactivity than in dull weather. Certainly radioactive substances have important physiological, physical, and chemical effects. They ionize the air, rendering it a conductor of electricity; they cause a fluorescence of certain chemical substances; they produce a sensation of light if they strike the eye; and if too active may cause destruction of living tissue. Substances so potent must have some physiological influence. Smoke. Smoke is a product of combustion and consists of a mixture of gases containing solid particles. Ordinary smoke consists largely of unburned carbon particles, hydrocarbons, and other pyroligneous products, gases, some of them poisonous, such as carbon monoxid, also mineral acids, etc. Angus Smith gives the following analysis of smoke from a common house fire: |