五十难曰∶病有虚邪，有实邪，有贼邪，有微邪，有正邪，何以别之？
然∶从后来者为虚邪，
从前来者为实邪，从所不胜来者为贼邪，从所胜来者为微邪，自病者为正邪。
此承上文五脏五邪之病，而辨其生克之义也。病有虚邪者，如心脏属火，其病邪从肝木传来，
木生火，则木位居火之后，是生我者，邪挟生气而来，虽进而易退，故曰从后来者虚邪也。病
有实邪者，如心属火，其病邪从脾土传来，火生土，则土位居火之前，是受我之气者，其力方
旺，还而相克，其势必盛，故从前来者实邪也。病有贼邪者，如心属火，其病邪从肾水传来，
水克火，心受克而不能胜，脏气本已相制，而邪气挟其力而来，残削必甚，故曰从所不胜来者，
贼邪也。病有微邪者，如心属火，其邪从肺金传来，火克金，金受克而火能胜，脏气既受
制于我，则邪气亦不能深入，故曰从所胜来者，微邪也。正邪者，如心脏止有自感之邪，而无
他脏干克之邪者是也。
何以言之？假令心病，中风得之为虚邪，伤暑得之为正邪，饮食劳倦得之为实邪，伤寒得之为
微邪，中湿得之为贼邪。
举心为例，以发明上文之义也。中风，肝木之邪也。得之，言因中风而心得病也。肝邪乘心，
是从后来者，故曰虚邪。伤暑得之，为心脏自病，故曰正邪。饮食劳倦得之，脾邪乘心，是前
来者，故曰实邪。伤寒得之，肺乘心，从所胜来者，故曰微邪。中湿得之，肾邪乘心，从所不
胜来者，故曰贼邪。余脏可类推，此病传五脏之生克也。
Difficulty 50 states: Diseases manifest as deficiency evil (Xu Xie), excess evil (Shi Xie), thief evil (Ze Xie), slight evil (Wei Xie), and proper evil (Zheng Xie). How are they distinguished?
The answer is: Evil transmitted from the generating organ behind comes as deficiency evil; evil transmitted from the generating organ ahead comes as excess evil; evil transmitted from the organ that does not generate me but controls me comes as thief evil; evil transmitted from the organ that I control comes as slight evil; and evil originating from the disease of the organ itself comes as proper evil.
This follows the preceding text regarding diseases of the five Zang organs and five evils, analyzing the principles of generation and restriction (Sheng-Ke). Regarding deficiency evil: for instance, the Heart belongs to Fire. If the pathogenic factor is transmitted from the Liver Wood, since Wood generates Fire, Wood is positioned after Fire. This represents "the one that generates me." The evil arrives carrying the vital energy of generation; although it advances, it is easy to recede. Therefore, it is called "deficiency evil transmitted from behind." Regarding excess evil: for instance, the Heart belongs to Fire. If the pathogenic factor is transmitted from the Spleen Earth, since Fire generates Earth, Earth is positioned before Fire. This represents "the one that receives my Qi." Its strength is vigorous, and it returns to exert influence; its momentum is necessarily strong. Therefore, it is called "excess evil transmitted from ahead." Regarding thief evil: for instance, the Heart belongs to Fire. If the pathogenic factor is transmitted from the Kidney Water, since Water controls Fire, the Heart is controlled and cannot overcome it. The Zang Qi is already mutually restrained, and the pathogenic factor arrives with its force, causing severe damage. Therefore, it is called "thief evil transmitted from the one that does not generate me but controls me." Regarding slight evil: for instance, the Heart belongs to Fire. If the pathogenic factor is transmitted from the Lung Metal, since Fire controls Metal, Metal is controlled and Fire prevails. Since the Zang Qi is already restrained by me, the pathogenic factor cannot penetrate deeply. Therefore, it is called "slight evil transmitted from the one that I control." Proper evil refers to cases where the Heart is affected only by self-induced pathogens, without interference or control from other Zang organs.
Why is this so? Suppose a Heart disease: contracting Wind-strike results in deficiency evil; contracting Summerheat results in proper evil; contracting due to dietary irregularities and fatigue results in excess evil; contracting Cold injury results in slight evil; contracting Dampness results in thief evil.
Taking the Heart as an example to elucidate the meaning above: Wind-strike is the evil of Liver Wood. Contracting it means the Heart becomes diseased due to Wind-strike. Liver evil invading the Heart comes from behind (in the generation sequence), hence it is deficiency evil. Contracting Summerheat constitutes a disease of the Heart itself, hence it is proper evil. Contracting due to dietary irregularities and fatigue involves Spleen evil invading the Heart, coming from ahead (in the generation sequence), hence it is excess evil. Contracting Cold injury involves the Lung invading the Heart, coming from the side that I control, hence it is slight evil. Contracting Dampness involves Kidney evil invading the Heart, coming from the side that controls me, hence it is thief evil. The same logic applies to other Zang organs. This illustrates the transmission of diseases among the five Zang organs through generation and restriction.