(2) The six exogenous pathogens may singly invade the body by a single pathogen and simultaneously and invade the body

by more th?n two pathogen. For example, common cold results frequently from pathogenic wind and cold; diarrhea is caused by pathogenic dampness and beat; bi-syndrome (arthralgia) is caused by pathogenic wind, cold and dampness and so on.

(3) They may be transformed into each other. Examples are: pathogenic cold in the body may be transformed into heat and

prolonged sumtmer-heat dampness may bring about dryness and fire to impair yin.

(4) The last feature of the six exogenous pathogens is that they invade the human body via the body surface or from the

mouth and nose or through both concurrently. This is known as "affection resulting from six exogenous pathogens."

The seven emotions refer to the human mental activities. In TCM, they are classified into seven classes: joy, anger, melancholy, anxiety, grief, fear and terror. They are the different responses to the environmental stimuli in the human body. In general circumstances, they belong to the normal physiological activities and wil not cause discases. When sudden, strong, long or protracted emotional stimuli go beyond the body's adaptability and endurance, the emotional stimuli will become pathogenic factors, which cause dysfunction of qi, blood and the zang- fu organs and imbalance of yin and yang, hence leading to diseases. This is known as "internal injury caused by the seven emotions".

The seven emotions are different from the six exogenous pathogens in causing diseases. The six exogenous pathogens, as mentioned above, usually invade the body through the skin, mouth and nose, and it is mostly exterior syndromes at the early stage of the onset. The seven emotions, however, directly affect the corresponding zang-fu organs to bring on diseases because a certain zang-fu organ is closely related to a certain emotional activity. S TCM says, "Anger impairs the liver; excessive joy impairs the heart; grief or melancholy impairs the lung, anxiety impairs the sple?n, and fright or fear impairs the kidney". The abnormal emotions mainly influence qi activity of the internal organs, so as to cause the dysfunction in ascending and descending of qi. Concretely speaking, "Anger causes the qi (to the liver) to ascend; joy makes the qi (of the heart) sluggish; sorrow makes the qi (of the lung) consumed; fear induces the qi (of the kidney) to dissipate; fright causes the disorder of the qi (of the heart); and anxiety brings about the depression of the qi (of the spleen)." As concerns other pathogenic factors such as pestilence, improper diet, maladjustment of work and rest, parasites, surgical trauma, phlegm retention, blood stasis, etc., we have to, though they are of equal importance, give them up on account of limited space.

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