Let us look at the components of healthy air. By air I mean that which is drawn in as breath, including all the bacterial and other life that may reside within it. The substance of air is good when it is not contaminated by extraneous matters, such as those listed above. Moreover, the air should be open to the sky, meaning not shut in by high mountains or confined in caves, high walls, or closed houses. Healthy air should be clear to the sight, which usually testifies to its purity. This is accomplished by winds blowing over the area, a process that continually cleanses the air.

    Closely related to the quality of air is the influence of the changes in the atmosphere that accompany seasonal and geographic variations. For example, a hot atmosphere (found in temperate and desert regions) disperses the natural force of the breath and has a relaxing effect. Too great a degree of heat results in a breakdown of the components of the blood and causes diseases of the yellow bile humor. It also causes sweating, diminishes the output of urine, impairs the digestion, and induces constant thirst.

    A cold atmosphere has a constricting effect, strengthens digestion, and increases the urine. It also causes the humors to lose their fluid characteristics, so that they are much more slowly broken down into their derivative components and are eliminated with difficulty. People sweat less in a cold atmosphere, and thus the elimination of toxins with perspiration is less. Cold also causes constipation because the anal muscles remain constricted, causing the feces to remain in the rectum longer than normal, so that the watery components are reabsorbed and passed into the urine.

    The seasons produce great changes in the body, and many diseases are primarily known by the season in which they occur. Spring is a healthy season, providing a temperament perfectly suited to the temperament of both blood and breath. It is in the spring that the humors--somewhat dormant over winter--begin to stir and disperse themselves more fully throughout the system, which often brings back the signs of chronic disease. People who overeat in the winter and exercise little are prone to springtime diseases.

    The diseases often common in spring include nosebleeds, inflammations, carbuncles, anginas, abscesses, aggravation of varicose veins, coughs, bronchitis, pneumonia, influenza, and measles. People in whom the phlegm humor predominates will show a tendency to apoplexy, paralysis, and arthritis. These effects are multiplied if the person undergoes extreme emotional conflicts or adds excess hot spices to the food, for this enhances the effects of the atmosphere on the person. The most effective means to avoid spring diseases, or lessen their severity, are purgatives, fasting or dietary restrictions, increasing fluids, and eliminating intoxicating liquors of all types.

    In the summertime the ground temperature is highest and the humors are dispersed, which impairs the faculties and natural functions. The blood and the blood humor are diminished in quantity (summer blood is said to be "thin"). Toward the end of summer, the black bile (atrabilious) humor increases. Older persons feel stronger in summer.

    In summer diseases run their course in a shorter period of time, because the warm air helps to disperse and mature disease-producing matter. But persons already weakened by a disease will find it worse in the summer, and may even lose strength and die. The wetter the summer, the more prolonged the disease. Ulcers, for example, will be harder to heal, and may spread and deepen. Diarrhea and loose bowels are common in summer, owing to the general flow of excess humors from the upper body into the lower body. This also explains why people traveling from winter climates to very warm climates (such as Mexico) experience diarrhea (even though it is usually blamed on contaminated food or water).

    The diseases generally associated with the hot season are fevers (especially continuing ones), emaciation, pains in the ears, eye problems, and furunculosis. For those living where there are southerly winds, deaths are highest in the summer months. Northerly winds are more favorable to health.

    Autumn produces many changes in the body, and much disease, for these reasons: (1) the temperature differences between daytime and nighttime are great; (2) the humors are spoiled by eating much fruit, by bad diet, and by accumulation of unresolved excesses within the interior of the body; (3) the general vigor of the body is impaired because of the effects of the preceding hot months.

    The disorders associated with autumn are fevers, enlargement of the spleen, scanty urine, impetigo, scabies, canker, pustules, angina, pulmonary afflictions, mental disease, diarrhea, sciatica, back and hip pain, and worms.

    It must be remembered that all of these conditions which we call disease are the result of the dispersal of the normal quantity and quality of the four humors. In the summertime, because of the heat, the amount of phlegm humor (and phlegm) increases. As the autumn cold comes on increasingly, the body cannot resolve those quantities of mucus rapidly enough. Fever arises as a special heat to rapidly process the excess phlegm into a thinner substance, which is then eliminated as perspiration and/or urine. Moreover, many people do not properly adjust their diet according to these seasonal changes, and thus there is most often an increase in the black bile humor and ashlike toxic by-products of digestion. With impaired and lessened sweating and other elimination, the accumulation of humors produces diseases, according to the inherent strengths and weaknesses of the individual's body.

    Generally, the autumn season will produce fewer diseases if it is very damp and rainy, because the moisture assists the expulsion of excess phlegm by softening it and making it more liquid. If this does not occur, the excess phlegm becomes hardened and may remain in the body over the winter season.

    Wintertime is better for digestion because people eat less. Also, the innate heat of the body is congealed within and fostered because the body responds to lower temperatures by increasing the internal heat. The disorders of winter are primarily associated with the phlegm. The blood humor is very plentiful in winter, and illnesses derived from blood humor imbalance are rarer.

    Inflammations of the nose and sinuses are common in winter, and, to a lesser extent, people experience pleurisy, hoarseness, and sore throat. Even rarer are pains in the chest and sides, chronic headache, mental problems, and epileptic seizures. All of these conditions are caused by an increase in the volume of the humors and by their being condensed and confined rather than dispersed. The elderly have the hardest time in the winter, while middle-aged persons enjoy winter the most.

    Many other factors connected with wind and atmospheric pressures influence general health. For example, it is said to be especially bad if a dry spring follows a dry winter, because the trees and foliage decay and produce poor feed for the animals, resulting in poor health for the people who eat them. The Chinese have gone so far as to elaborate a system of evaluating the effects of massive disturbances in the atmosphere caused by such phenomena as hurricanes, earthquakes, and tornadoes.

    The influence of the atmosphere and seasonal changes has direct and profound effects on the foods growing in the soil and receiving nourishment from the rain. The growth patterns of fungi in various kinds of soil depends on the degree of cold and wetness. An observant and knowledgeable physician ought to be aware of these events of nature and be prepared to include them in evaluation of the patient.

    Moreover, there are other factors that indirectly contribute to the quality of the air and atmosphere, such as the types of trees, mines and mineral deposits, cemeteries, dead animals, putrid water, day soil, and muddy swamps.