The kidney governs water and stores essence. It governs storage (in a wider sense) and absorbs qì. It is the root of the yīn and yáng of the entire body. It governs the bones and engenders marrow. It opens at the ears and has it bloom in the hair. It stores mind/memory, its mind is fear, and its voice is groaning. It stands in exterior-interior relationship with the bladder. It holds the Office of Forceful Action.

Water

Water is vital to life. Even our bodies are nearly 70% water. A human can only survive for a couple of days without this precious substance.

Water also has the quality of cold. Even in summer, it tends to remain cool. This is because, as modern science tells us, water has a high specific heat capacity, which means a lot of heat is needed to warm it up. Therefore, in summer the ocean takes longer to heat than the land.

Water moistens and descends (水曰润下 shuǐ yuē rùn xià): The water phase is classically described as having the qualities of moistening and descending. Moistening reflects the water’s life-nurturing effects. Descending refers to the fact that it descends to low places and gravitates to low ground, where it finally becomes still. In the rain cycle, water in the earth evaporates and rises into the sky to form clouds. It then turns into water and falls as rain to moisten the earth to provide nourishment for plant and animal life. Accumulating in streams and rivers, it flows downward to eventually reach the ocean.

North, night: North is the position of the sun when in the daily cycle the sun reaches its lowest position in the sky, hiding away to provide no light or warmth. Nighttime is the darkest, coldest, and stillest time in the daily cycle. In the northern hemisphere, northern places are darker and colder than southern places. North and night naturally correspond to water because they share with water the qualities of darkness, cold, and descent. These are all yīn qualities, making water the most yīn of all the phases.

Winter, storage: Wintertime is the part of the yearly cycle that corresponds to nighttime in the daily cycle by the reduced amount of sunlight. Since cold, stillness, and nurturing are all yīn qualities, the water phase is associated with winter, the coldest season, when activity in nature, as symbolized by yáng qì, reaches its lowest ebb and many life forms are reduced to inactive forms. In winter, water reaches its lowest temperature and turns to ice, finding its ultimate and total stillness. Animals are in hibernation, deciduous trees are leafless, and many plants survive only in seed or root form. Winter therefore has the qualities of dormancy or latency, which, again, are yīn qualities. These qualities are summarized in the concept of 藏 cáng, which means storing or hiding. Winter storage is the deepest and quietest form of nurturing. The nurturing quality of winter is something that farmers are very much aware of. They know a good harvest follows a cold snowy winter (瑞雪兆丰年 ruì xuě zhào fēng nián).

Black is the color associated with the water phase. We might speculate that the color black is associated with water because of the lack of sunlight in winter and the blackish appearance of water in winter landscapes. One might well have expected white to be the color corresponding to winter, given that winter is the season of snow. However, color associations seem to be based on the season in which a color first appears, which, in the case of white, is autumn.

Saltiness is the flavor associated with water: When water in the environment reaches the ocean, it becomes salty. Salt leaches water out of vegetables and meats. It works as a preservative for vegetables and meats, enabling them to be stored for the winter when fresh foods are scarce. Furthermore, empirical evidence taught that certain salty medicinals act on the kidney, the viscus associated with the water phase.

Five-phase cycles: In the engendering cycle, water engenders wood, since it is needed for plants to grow. It is engendered by metal because water condenses on metal. In the restraining cycle, water restrains fire, since fire can be doused by spraying water on it. Water is restrained by earth because earth can dam the flow of water.

The Kidney

The main functions of the kidney are governing water and storing essence. The kidney is located in the lower burner and is the lowermost of the five viscera, corresponding to north, where the sun reaches its lowest position. Students are reminded of this when they encounter the method of treatment called draining the south and supplementing the north (泻南补北 xiè nán bǔ běi), that is, draining the heart and supplementing the kidney.

The kidney governs water refers to the urination function. Gross dissection would have enabled early medical scholars to trace the urinary tract from the meatus to the bladder, and from the bladder to the kidney, the original source of urine. Such anatomical knowledge would explain why the kidney is paired in exterior-interior relationship with the bladder, which is a discharging organ that dispatches urine out of the body.

Although medical scholars identified urine production as a function of the kidney, the paucity of information provided by direct observation forced them to apply analogical thinking. The urinary function came to be understood by analogy to a pot of water over a fire. In this image, fire represents kidney yáng, which heats fluids so that the clear part is distilled out and returned into the system, leaving the turbid part to drain off as urine.

The kidney stores essence: By analogy to the way in which life is stored in the form of seeds and roots in winter, the kidney was expected to reflect the storage quality of winter. Although all the viscera are storehouses that therefore store certain things, the idea of storage in the context of the kidney has a special meaning because the kidney stores the essence of life, i.e., human life in its latent form.

The Chinese word for essence is 精 jīng. The character has a rice radical (米), suggesting the idea of choice grains, that is, the best sample of something. One form of essence is semen, which in our culture is described as the male seed of human life (the Latin word semen simply means seed). Although the Chinese word for essence reflects no association with seed, descriptions of conception-enhancing formulas are often expressed in metaphors such as planting seeds and planting progeny.Semen is discharged from the urinary meatus, the same opening from which urine is discharged. Since urine originates from the kidney, it would have been quite reasonable for early medical scholars to think that the watery substance semen

also originated in the kidney or was somehow related to it. This, however, is speculative since they knew that castration rendered a male infertile. They were aware that conception occurred because of the union of male and female essences, and they would naturally have thought that watery vaginal and vulvar secretions were the female equivalent of the male essence.

Be that as it may, the essence spoken of in Chinese medicine is responsible not only for reproduction but also for the development of the individual and for the natural decline in old age, and hence can be viewed as the life potential. Functionally, it therefore bears some similarity to the modern concept of DNA, which of course the ancient Chinese had no way of detecting. In Chinese medicine, these notions are modeled on the end of the natural cycle in the winter. The reproductive function of essence is the life potential that ensures survival through progeny. Its control over development and its power to resist the aging process gives the individual the best chances of surviving into old age. As many examples will show, the kidney can be described as the life-and-death viscus.

The kidney is the root of earlier heaven: The essence stored by the kidney is earlier-heaven (congenital) essence, which an individual receives from their parents before birth and which can be partly replenished by later-heaven (acquired) essence, i.e., nutrients absorbed by the spleen. Since full replenishment is not possible, every individual’s lifespan is limited.

The kidney governs storage: The kidney not only stores essence but also has a general storage, or more precisely, a retention function that prevents the abnormal loss of urine, stool, semen, vaginal fluids, and fetuses. This is a container metaphor, whereby the breakdown of the function results in spillage of some kind.

This storage function works in complementary opposition to the liver’s free coursing function. The liver promotes movement, while the kidney inhibits it. Impairment of the kidney’s function of inhibiting flow, called insecurity of kidney qì, can result in frequent urination, profuse urination at night, urinary incontinence, excessive menstruation, miscarriage, copious vaginal discharge, premature ejaculation, or seminal loss. Impairment of the liver’s function of free coursing, called depressed liver qì, can cause menstrual pain, menstruation at irregular intervals, or amenorrhea.

The kidney governs the bones and engenders marrow: When a person ceases to live, as nature ceases to be active in winter, the flesh soon decomposes leaving only the bones. Just as trees are stripped of leaves in winter, so the bones are stripped of flesh in death. Marked changes in the hardness of the bone closely follow the development of essence from birth to death. Bones are soft at birth, are strongest in the prime of life, and become brittle with advancing age.

Bones themselves are hollow and contain, or store,marrow, so they share the kidney’s attribute of storage, which reflects a container metaphor. The skull is a large bony structure that contains the brain, which early medical scholars regarded as the sea of marrow, again sharing the quality of storage.

The teeth are the surplus of the bones: Like the bones, the teeth are made of hard white material and they contain pulp as bone contains marrow.

The brain is the sea of marrow (脑为髓之海 nǎo wéi suǐ zhī hǎi): To the surprise of many Westerners, Chinese medicine has little to say about the brain. The control center for emotions, mental activity, and even control over and coordination of physical functions is said to be, not the brain, but the spirit stored in the heart. Traditional statements about the brain are scant.

Nevertheless, as the sea of marrow, the brain falls within the realm of the kidney. Kidney essence is closely related to mental faculties, since abnormalities in the mental development of children and dementia in adulthood are explained in terms of insufficiency of kidney essence (see the kidney stores mind further ahead). In fact, the spirit stored in the heart, is often referred to as the essence-spirit (精神 jīng shén), reflecting the notion that it is reliant on essence. Stored by the kidney, which is the most yīn of the viscera, essence can be understood as the yīn counterpart of the spirit, which, belonging to the heart, is yáng. Essence-spirit expresses the natural yīn-yáng duality of mental functions.

Although it is kidney essence rather than the brain that is closely associated with mental function, the status of the brain has been the subject of controversy ever since Lǐ Shí-Zhēn of the Míng Dynasty introduced the idea that the brain is the house of the original spirit (脑为元神之府 nǎo wéi yuán shén zhī fǔ), not the heart. Such claims never prompted a thorough revision of medical theory, even though over recent centuries Chinese medicine has constantly faced the bitter challenge of Western medical ideas. We can only speculate on the reasons why the brain was never accorded greater importance. It may be that a special interest in the animating qualities of the spirit trained Chinese focus onto the beating heart. Maybe the brain’s functions were too difficult to probe. Perhaps, in the traditional intellectual climate of China, where the ancients were always revered, any challenge to the heart as sovereign might have been regarded as incitement to political subversion. An illuminating discussion of this issue is provided by Ning Yu (於宁).

The kidney is the root of the yīn and yáng of the entire body: This statement derives from the notion that since the kidney stores essence, it also holds reserves of yīn and yáng. It is borne out in the clinical observation that whatever viscus yīn or yáng vacuity may affect, kidney signs are usually also detectable, notably reproductive and sexual dysfunctions, as well as limp aching lumbus and knees.

The kidney is averse to dryness: This is not taken to mean that it is susceptible to externally contracted dryness. Rather, it refers to the fact that the weakening of kidney essential qì in old age is characterized by scant semen, cessation of the menses, dry and brittle bones, and loss of suppleness of the body. Aversion to dryness reinforces the notion that the kidney governs water.

Spittle is the humor of the kidney: Spittle (唾 tuò) is the thicker and frothier of two kinds of saliva, the other being drool, which is associated with the spleen (see Spleen, Earth, Office of the Granaries above).

While drool is associated with the spleen by the natural connection of the mouth to the digestive tract, spittle is attributed to the kidney because network vessels of the kidney pass through the underside of the tongue on either side, allowing liquid derived from kidney essence to issue there. In accordance with this theory, excessive or extended production of spittle is believed to deplete kidney essence. For this reason, qì-gōng practitioners swallow their spittle to nurture and preserve their kidney essence. The fact that kidney yīn vacuity may be characterized by a dry mouth may have been a further factor in the development of this theory.

The distinction between two types of saliva according to differing viscosity may have been encouraged by yīn-yáng theory. The association of spittle with the kidney and drool with the spleen may also have been fostered by the contrast between the spleen as the root of later-heaven (acquired constitution) and the kidney as the root of earlier-heaven (congenital constitution).

The distinction between thicker and thinner forms of saliva has rough correspondences in biomedicine, which distinguishes between serous, mucous, and seromucous forms. The sublingual salivary glands produce mostly mucous saliva, whose main function is lubrication. The parotid and submandibular glands, by contrast, produce serous saliva that contains amylase, which aids digestion by breaking down starch. This would suggest that spittle corresponds to the saliva produced by the sublingual glands, while drool corresponds to that secreted by the parotid and submandibular glands.

The kidney governs qì absorption: The lung helps the depurative downbearing function of the lung to draw qì into the body. Elderly people, for example, who naturally tend to suffer from kidney vacuity, often experience breathing difficulties attributable to the kidney failing to absorb qì. The lung belongs to metal, while the kidney belongs to water, and so lung-metal engenders kidney-water. Lung-metal supports kidney-water, as a mother gives birth to and nourishes a child. Yet, this relationship is characterized not only by the mother’s providing nourishment but also by the child’s ability to take the nourishment, as by taking milk from the breast. The kidney’s function of qì absorption can be likened to the child suckling from the mother’s breast.

The kidney opens at the ears: Kidney essence is associated with aging. People tend to lose their hearing in old age, and this is traditionally treated as insufficiency of kidney essence. However, many functions of the body decline in old age, so one might wonder why hearing, in particular, should be associated with the kidney. The most likely explanation lies in inverse association between winter and sound. Winter is the most silent season of the year. It is animals, birds, and insects that create the most noise in nature. However, in northern parts of China, winter is a time when many animals are in hibernation, most birds, with the partial exception of the black crow, have migrated southward, and most insects are not active. The deafness of old age reflects the silence of winter when nature is inactive.

The kidney stores mind: The Chinese word translated here as mind is 志 zhì. The composition of the character suggests the direction of the heart. This word has many distinct uses, including will, inclination, determination, ambition, aspiration, purpose, emotion, state of mind, memory. Hence, its meaning in the context of the kidney has been the subject of much discussion. The prevailing view among scholars is that it refers to the basic mental faculties that enable a person to set and consistently work toward specific goals.

Another view is that 志 zhì as the mind of the kidney refers specifically to memory. According to this view, 志 zhì is used in the sense later distinguished in writing as 誌 zhì (and de-distinguished in the modern simplified script). Memory can be seen to be related to the kidney in several ways. It tends to be lost in old age with the depletion of kidney essence. Understood as the faculty that stores experience, it can naturally be subsumed to the storage function of the kidney. Furthermore, memory can be understood as the mental counterpart of essence, which is the biological memory required to reproduce human, and indeed all forms of life. Given the association of the kidney with the survival of life after the yearly cycle of nature ends, individuals survive after death in the memory of those who knew them. Nevertheless, it should be noted that forgetfulness (poor memory) in modern practice is associated as closely with the heart as with the kidney.

The two interpretations are not incompatible, since memory is necessary for the consistent pursuit of a goal and its decline often observed in old age makes the pursuit of any task difficult. Mind is the preferred translation because it captures the wider interpretation without excluding the narrower one.

Sleep disturbances in Chinese medicine are mostly attributed to the heart or the kidney. A pathological condition with profuse dreaming usually indicates a heart problem, while one marked by dreamless sleep indicates a kidney problem. This again reflects the absence of activity associated with winter.

Fear is the mind of the kidney: Note that here the word mind has a meaning different from mind in the phrase the kidney stores the mind. Here it denotes emotion or mindset, as in the five minds associated with the five viscera.

Fear (恐 kǒng) is felt not only in the upper part of the body but also in the lower regions of the trunk where the kidneys are located. Fear is associated with the water phase by virtue of the qualities of winter. Fear in its extreme form is fear for one’s life, and winter is the time of year when all life is threatened. In harsh northern climes, winter is the season when people in traditional agrarian and pre-agrarian societies were pressed by food shortages and by lack of warmth. Even today, the cold weather of winter represents a threat particularly to the aged and many life forms.

Fear also has a direct association with the kidney, since it affects the general storage function. Severe fear or fright can cause both urinary and fecal incontinence. Hence, it is said that fear damages the kidney.

Of interest here is that, in modern medicine, fear is known to severely weaken the immune system. The effects of fear on general health may not have escaped the attention of early medical scholars. We know that as people’s physical and mental vigor decline in advancing years and they become increasingly dependent on others, they begin to fear many things that they would not have feared in their younger years.

Groaning is the voice of the kidney: This accords with fear and impending death.

Office of Forceful Action

The kidney holds the Office of Forceful Action; dexterity and ingenuity arise from it. The interpretation of this phrase from the Nèi Jīng has been the subject of debate. Zuò qiáng zhī guān 作强之官 can be most literally translated as official for forceful action. Taken to refer to a government position, it would correspond to the modern notion of ministry of labor. However, the term does not appear to have been used other than in the Nèi Jīng. Jì qiǎo 技巧, here translated dexterity and ingenuity, can refer to physical agility and dexterity or to mental skill and ingenuity (agility in A Practical Dictionary of Chinese Medicine). Early Nèi Jīng commentator Wáng Bīng suggests that the whole phrase refers to skills (jì qiǎo) in women and to forceful action (zuò qiáng), i.e., physical strength, in men. Others do not follow the division between the sexes, pointing rather to the connection between physical strength and the condition of the bones and marrow or to the connection between physical strength and reproductive capacity.

The disagreements are arguably of little consequence. The notion of the kidney’s storage function in its widest sense concerns the preservation of the life force in decline. In old age, people lose not only their reproductive capacity, but also their physical strength, their agility, and their mental faculties (remember, the kidney stores the mind), making them unable to do physical or mental work. Maintaining the ability for physical and mental activity in advancing years is a sign of an abundance of kidney essence. The relationship of the kidney to mental agility and to bone and marrow is reflected in the head being described as the house of bright essence (精明之府 jīng míng zhī fǔ).

Summary of Kidney-Water

The kidney belongs to water and governs water (producing urine). It governs the bone and engenders marrow, opens at the ears and the two yīn, and has its bloom in the hair. Its humor is spittle, and its mind is fear. It holds the Office of Forceful Action.

• Responsible for producing urine, the kidney governs water and hence belongs to the water phase.
• Storing essence derives from the association of winter with the water phase, a time when nature is silent and inactive, storing resources for warmer weather. Essence controls reproduction, development, and aging. The kidney also has a general storage function, preventing the loss of urine, stool, semen, menstrual blood, and fetuses.
• The connection with the bones (which store marrow), the brain (marrow stored in the skull), mind (mental faculties) including memory (memories are stored experiences) further reflect the storage function.
• The ears being the outer orifice of the kidney is related to the loss of hearing in old age, which resembles the silence of winter.
• Fear is associated with the kidney because fear and fright impair the storage function, causing incontinence, and because death, the thing we fear most, is the end of the human cycle as winter is the end of the seasonal cycle in nature.
• The kidney holds the Office of Forceful Action, reflecting the observation that the ability to work physically or mentally relies on the health of essence.