Wood of Metal: Zhi Shi 枳實

味酸皆屬金，五味[子]為之主，枳實為木，豉為火，芍藥為土，薯蕷為水。

All sour belongs to metal, for it is governed by Wuweizi; Zhishi is wood, [Dan Dou ]Chi is fire, Shaoyao is earth, and Shuyu [Shanyao] is water.

Zhishi is the unripe fruit of the bitter orange (Fructus aurantii immaturus). It’s placement here as the Wood of Metal might seem a bit puzzling at first. It's bitter orange, after all, not sour orange! So why is it being classified as belonging to Metal?

Sometimes classical herbalists see a Chinese herb differently from more modern practitioners, and when we encounter a discrepancy between how an herb is classified in TCM and how the Tang Ye Jing classifies herbs, it can be instructive to look at older texts, like the Shen Nong Ben Cao Jing (神農本草經):

枳實 味苦寒。主治大風在皮膚中如麻豆苦癢，除寒熱熱結，止利。長肌肉，利五臟，益氣輕身。生川澤。

Zhishi: Its flavor is bitter and cold. It governs treating great wind within the skin causing severe itching as if caused by hemp seeds, removes cold and heat hot knotting and stops diarrhea. It promotes growth of flesh and muscle, benefits the five zang, increases qi and lightens the body. It grows in rivers and marshes.

Image c/o TCM Wiki

In this case, both contemporary TCM and the classical source texts agree on the flavor and nature of Zhishi. So the question remains: what does this bitter herb have to do with Sour and Metal? And what does it mean to say that it is the Wood of Metal?

Contemplating this question will help us better understand the clinical uses of Zhishi, as well how the TYJ classifies herbs.

Let’s consider the action of bitter: we know from the introduction that according to the Neijing, bitter hardens or consolidates (堅). But bitter also drains downward. This downward movement also belongs to Metal, which descends as well as gathers. One of the main functions of the Lung, as the Metal zang, is the descent of qi and fluids. 

The descending action of Lung qi is also responsible for pushing out waste through its paired fu organ, the Large Intestine. In terms of the activity of the Six Conformations, Dry Metal belongs to Yangming, whose activity of closing (合) can also be understood as a kind of descent. This conforms with the physiological function and direction of the “Stomach Family” (胃家) in taking in food and pushing it through the body via peristalsis.

From the perspective of season and direction, Zhishi belongs to Metal because it descends.

What does it mean to say that it belongs also to Wood, or that it is the “Wood of Metal”? One way of understanding this is that it mediates the relationship of Metal to Wood. In terms of the Five Phases, the Lung’s descent balances the ascent of the Wood zang, the Liver, which is in charge of ascending qi. We know that Metal Controls Wood via the Controlling Cycle. When Wood is excessive, it is checked by the descending mandate of Metal. 

Through its activity of descending, Zhishi can check the excessively upbearing activity of Wood by promoting the activity of Metal. When the Shen Nong Ben Cao Jing says that it treats knotting (結), we can understand this to be referring to the knotting of qi that occurs from constraint when Liver Wood is in excess. Zhishi can cut through this by descending, in effect we might say this is helping Metal to control Wood.

If this seems abstract, let’s consider some famous formulas that employ Zhishi. Commonly, Zhishi is employed in formulas when there is considerable qi stagnation in the chest and abdomen, and more specifically, within those cavities of the chest and abdomen that belong to Yangming, and thus to Metal.

We can see this when it is paired with Baishao (the Earth of Metal) to form Zhishi Shaoyao San (枳實芍藥散). In the Jin Gui Yao Lue, this two herb formula was indicated for abdominal fullness and vexing pain in postpartum women (產後腹痛煩滿) and it is often used as a relatively gentle way to treat to constipation. Zhishi breaks through abdominal knotting and promotes the descending of the Yangming, promoting bowel movements, while Baishao soothes, softens and moistens.

From a Five Phase perspective, we can understand this as involving a disharmony between Wood and Metal, which is in turn affecting the Earth Phase.

In addition to Zhishi and Bai Shao, Si Ni San contains Zhi Gan Cao (thereby incorporating Shao Yao Gan Cao Tang, a formula we will explore when we look at Bai Shao Yao) as well as Chai Hu. Zhishi performs the same functions of descending through the Yangming spaces to move through stagnation, while Bai Shao soothes and nourishes Jueyin Wood, but Zhishi’s activity also synergizes with Chai Hu as well as Bai Shao. Chai Hu has an overall lifting action, which balances Zhishi’s descending action. If we wanted to consider this in terms of the zang fu, we can understand Chai Hu as acting more on the Liver, while Zhishi acts on the Gallbladder.

Chaihu promotes the upbearing activity of the Liver, while Zhishi promotes the downbearing activity of the Gallbladder. Balancing the upbearing and downbearing activity of the Wood zang and fu in turn helps to balance the upbearing and downbearing of the central pivot of the Spleen and Stomach. Regulating ascending and descending in this fashion is one characteristic of the harmonizing method (和法) in Chinese herbalism.
Other formulas that demonstrate the descending activity of Zhishi are the Cheng Qi Tang (承氣湯) family of formulas, which emphasize Zhishi’s action on the Yangming organs well as Wen Dan Tang (溫膽湯), which emphasizes its ability to descend the Gallbladder.
Hopefully by now it’s clear why Zhishi is grouped with Metal, and also what it means to say that it is the Wood of Metal.

What’s important to pay attention to is the qi dynamic. Zhishi belongs to Metal because it descends, and therefore, its action accords with the basic direction of Metal. By descending, it is able to carry the relationship of Metal to Wood.This basic and essential dynamic helps us to understand literally all of Zhishi’s abilities, and its role in the dozens of classical formulas it occurs in.

We can conceptualize Zhishi as affecting the Gallbladder, or the various organs and tissues belonging to Yangming. We can remember that it treats various bindings and knottings of qi, and we can also consider its effect on substances like phlegm. All these ways of conceptualizing its action are useful in various contexts, but they are all derived from understanding the basic direction and dynamic of Zhishi. That directional dynamic is completely described by the statement that Zhishi is the Wood of Metal.

Grasping this principle and applying it in a fluid way enables us to use Zhishi clinically, and it also demonstrates the elegance and power of a classical approach to herbalism.