凡此诸病，是以言脏腑十二经脉所受虚实之证，所谓标也。为其病者，寒暑燥湿风火之气，
所为本也。夫六气之用，己胜则克其妻，己衰则夫来克者，淫治之纪也。大抵腑脏之气，以平而
为期，气盛则行其胜也，无问夫妻子母，乘虚而感之，生其病也，实感过极，而亦自病矣。气虚
者受邪，无问相生相克，但感其邪，而病由生也。夫五行之道，正则和平，而递元相生相济，否
则邪生，元相克伐，故有虚邪、实邪、贼邪、微邪、正邪。而此之五邪也，然虚邪者，谓母邪乘
其子而病也。假令风木行胜，则肝气有余，心火感而以生其病。然风木行胜，则土气自衰，土衰
不能制水则水盛，水盛制火，而心不能实，故曰虚邪也。实邪者，谓土来乘火，而心病也。然土
胜则水衰，水衰不能制火则心火自盛，故曰实邪也。贼邪者，谓水来乘火，而心病也。然水能克
火，故曰贼邪也。微邪者，谓金来乘火，而心病也。然火能克金，故曰微邪也。正邪者，谓心火
有余，而自生其病也。然无相下，故曰正邪。余仿此推之。凡此五邪，各有微甚。至微者，微邪
也。次甚者，实邪也。其次者，正邪也。更次者，虚邪也。至甚者，贼邪也。欲知五邪之要，必
明脉与病气，而以受病腑脏经脉参合，推其五行相生相克，昭然可知矣。大凡病生之处谓之标，
为病之气为之本也。
（新添）夫受病之由者，或从外而得者，或从内而得者。其六气为病者，乃风火寒三气，皆
外感而得者。所为邪风似箭，玄府开张，风寒暑感于皮毛，在于腠理，入于卫，乃肺经所受也。
或风池、风府、口鼻而入，未入于营，当有汗，可以解肌而已。或入于营者，属心，无汗，当发
汗而已也。若燥湿热三气者，或饥饱劳损，忧愁虑恐悲恨，蛊
毒魑魅，皆内感而得者。经曰∶从外而得者治其外，从内而得者治其内。从外而得，盛于内者，
先治其外，然后治于内。从内而得，盛于外者，先治其内，然后治于外。不在内，不在外，治于主病。
The aforementioned diseases refer to the deficiency and excess syndromes experienced by the Zang-Fu organs (Viscera) and the twelve meridians, which is termed the "Biao" (Manifestation/Root of manifestation). The pathogenic factors of Cold, Heat, Dryness, Dampness, Wind, and Fire (Six Qi), which cause these diseases, constitute the "Ben" (Fundamental Cause/Etiology).
Regarding the interaction of the Six Qi: when one Qi is in excess, it overacts upon the Qi it controls (the controlled element); when one Qi is deficient, it is overacted upon by the Qi that controls it (the controlling element). This is the principle of pathogenic invasion. Generally, the Qi of the Zang-Fu organs achieves health through balance. When a Qi is in excess, it exerts its controlling influence, regardless of whether this relationship corresponds to the controlling (husband-wife) or controlled (child-mother) relationships in Five Phase theory. If such an imbalance invades due to deficiency, disease arises. If the pathogenic influence is extreme, it may even cause self-damage to the organ itself. When the Qi of the organs is deficient, it is susceptible to pathogens; regardless of the generative or controlling relationships among the Five Phases, once the pathogen is contracted, disease ensues.
The way of the Five Phases (Wu Xing), when normal, maintains peace and proceeds through mutual generation and assistance. When abnormal, pathogens arise, leading to mutual overacting. Thus, there are five types of pathogens: Xu-Xie (Deficiency Pathogen), Shi-Xie (Excess Pathogen), Zei-Xie (Thief Pathogen), Wei-Xie (Minor Pathogen), and Zheng-Xie (Direct Pathogen).
"Xu-Xie" refers to disease caused by the mother organ's pathogen invading the child organ. For example, if Wind-Wood is in excess, Liver Qi becomes hyperactive. Heart Fire is affected and diseased. However, excessive Wood overacts on Earth, causing Earth Qi to decline. Declining Earth cannot control Water, leading to Water excess. Excessive Water overacts on Fire, preventing Heart Qi from being sufficient. Hence, it is called "Xu-Xie."
"Shi-Xie" refers to disease where Earth overacts on Fire, causing Heart disease. Since Earth is in excess, Water declines. Declining Water cannot control Fire, causing Heart Fire to become naturally excessive. Hence, it is called "Shi-Xie."
"Zei-Xie" refers to disease where Water overacts on Fire, causing Heart disease. Since Water controls Fire, this direct overaction is termed "Zei-Xie."
"Wei-Xie" refers to disease where Metal overacts on Fire, causing Heart disease. Since Fire controls Metal, this weak counter-reaction is termed "Wei-Xie."
"Zheng-Xie" refers to disease arising directly from Heart Fire excess without interference from other organs' pathogens. Hence, it is called "Zheng-Xie." Other cases can be deduced similarly.
These five pathogens vary in severity. The mildest is Wei-Xie; next is Shi-Xie; then Zheng-Xie; followed by Xu-Xie; and the most severe is Zei-Xie. To understand the essence of these five pathogens, one must clarify the pulse and pathogenic Qi, integrate them with the affected Zang-Fu organs and meridians, and deduce the Five Phase interactions, which will make the situation clear. Generally, the site or manifestation of the disease is the "Biao," while the pathogenic Qi causing the disease is the "Ben."
(New Addition)
The causes of disease may originate externally or internally. Among diseases caused by the Six Qi, Wind, Fire, and Cold are all acquired through external contraction. Pathogenic wind strikes like an arrow, opening the Xuanfu (sweat pores). Cold, Wind, and Summerheat invade the skin and hair, reside in the Couli (interstices), enter the Wei (Defensive) level, and affect the Lung Meridian.
If pathogens enter via Fengchi (GB20), Fengfu (GV16), or the nose and mouth, but have not yet entered the Ying (Nutritive) level, sweating should occur, and the condition can be resolved by releasing the muscle layer (Jie Ji). If pathogens enter the Ying level, they belong to the Heart; there is no sweating, and the condition requires inducing sweating (Fa Han).
Regarding Dryness, Dampness, and Heat, these are often caused internally by irregular diet (hunger or overeating), physical exhaustion, or emotional disturbances such as worry, anxiety, fear, grief, and resentment, as well as by toxins or supernatural influences. These are acquired internally.
As stated in the classics: "Diseases acquired externally should be treated externally; diseases acquired internally should be treated internally." If a disease originates externally but manifests strongly internally, treat the exterior first, then the interior. If a disease originates internally but manifests strongly externally, treat the interior first, then the exterior. If the disease is neither strictly internal nor external, treat the primary organ responsible for the pathology.