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Chinese Yam (Dioscoreae Rhizoma), sweet in flavor, neutral in temperature, non-toxic. It enters the Taiyin organs of the hand and foot meridians (Lung and Spleen), and can also enter the Spleen and Stomach. It treats various deficiencies and hundred damages, benefits Qi and strength, opens the orifices of the Heart, enhances wisdom, and is particularly good at stopping nocturnal emissions, strengthening the Spleen, promoting appetite, stopping diarrhea, and generating essence. Chinese Yam can serve as either a sovereign drug or an assistant drug; there is no unsuitable use for it. Using more yields benefits, using less also yields benefits, and since ancient times to the present, there has been little dissent. However, I alone have slight reservations because it overly strengthens the Spleen. People suffer from weak Spleen function; if the Spleen is strengthened, the Large Intestine will surely become firm, and Stomach Qi will surely become strong with good appetite. Why single it out for criticism? One must not realize that when Spleen and Stomach Qi are too weak, Chinese Yam must be used to strengthen them; but if Spleen and Stomach Qi are already too vigorous, using Chinese Yam will make them excessively strong, potentially stirring up Fire. Often, people experience chest and abdominal fullness and distension, which worsens after taking Chinese Yam; this is precisely because it aids the excessive vigor of the Spleen and Stomach. People do not know this is the fault of Chinese Yam but blame other herbs; this stems from a lack of understanding of the principles of herb properties. Generally, Chinese Yam enters the Heart, guiding pathogenic factors from the Spleen and Stomach to easily enter the Heart. Chinese Yam tonifies deficiency but can also tonify excess, thus causing increased fullness and distension. Since the world believes Chinese Yam has merits without faults, I point this out specifically, not to disparage Chinese Yam. Apart from this, there is nothing else to discuss regarding Chinese Yam.

One asks: Chinese Yam is a substance that tonifies Yin and Essence, yet you say it is a product for strengthening the Spleen and Stomach. Why do you like to be different? I reply: Chinese Yam benefits people infinitely, and harms them rarely. When discussing Materia Medica, I wish for its merits and faults not to obscure each other. Chinese Yam has merits without faults. To say it can aid Spleen and Stomach Fire is seeking faults within its merits. However, among all people, those with overly vigorous Spleen and Stomach are one or two in a thousand. One cannot cling to the theory of "stirring Fire" and generally suspect that those with unvigorous Spleen and Stomach should also use it cautiously. If Spleen and Stomach are unvigorous, Kidney Qi must be weak; strengthening the Spleen and Stomach is precisely how one tonifies Yin and Essence. I speak of the general rule; what is there to be different about?

One asks: Chinese Yam tonifies the Kidney, which is why Master Zhang Zhongjing used it in Liuwei Dihuang Wan (Six-Ingredient Pill with Rehmannia). However, Chinese Yam truly can strengthen the Spleen and promote appetite. Is Liuwei Dihuang Wan not solely a medicine for tonifying the Kidney? I reply: Liuwei Dihuang Wan is indeed a medicine that directly tonifies Kidney Water. Chinese Yam is also a medicine that tonifies Kidney Water. How can there be doubt in their mutual assistance? However, the meaning of using Chinese Yam in Liuwei Dihuang Wan lies entirely elsewhere. Chinese Yam is a herb that enters no meridian without entering the Heart, Liver, Spleen, Lung, and Kidney. Although Liuwei Dihuang Wan directly tonifies Water in the Kidney, Kidney Water must be shared by the Five Zang Organs. Without guides to lead between the Five Zang Organs, how can the water be distributed to moisten them all? If one were to use separate assistant drugs for the Five Zang Organs, the formula would inevitably be mixed and impure. Therefore, it is better to use Chinese Yam to tonify Water in the Kidney while simultaneously penetrating all Five Zang Organs. This is Zhang Zhongjing’s strategy of tonifying one while attending to five, possessing a mechanism difficult to fathom even by spirits. ([Commentary] Chinese Yam tonifies Water and penetrates the Five Zang Organs. Master Zhang Zhongjing’s use of it in Liuwei Dihuang Wan relies on this prescription, lacking this profound discussion.)

One asks: I have heard the meaning of Chinese Yam entering Liuwei Dihuang Wan. Is there also a rationale for its entry into Bawei Wan (Eight-Ingredient Pill)? I reply: Bawei Wan is an augmentation of Liuwei Dihuang Wan. It seems that knowing Liuwei Dihuang Wan allows one to know the meaning of Bawei Wan. Who would expect that the use of Chinese Yam in Bawei Wan holds another profound meaning? Liuwei Dihuang Wan tonifies Water in the Kidney. Bawei Wan, however, tonifies Fire in the Kidney. Tonifying Fire in the Kidney means tonifying the Ministerial Fire of the Mingmen (Gate of Life). There are two Ministerial Fires in the body: one in the Kidney, one outside the Heart. If one tonifies the Ministerial Fire in the Kidney, the Ministerial Fire outside the Heart will inevitably contend. Contention leads to chaos; thus, one must prepare to pacify it. If one tonifies Fire below, one must also tonify Fire above (in the Heart). However, if one tonifies below due to Cold in the Kidney, and attends to Heat in the Heart by tonifying above, let alone failing to warm the Cold below, the above may turn into Heat. The complexity of medication usage is lamentable. The brilliance lies in using Chinese Yam in Bawei Wan. Chinese Yam enters the Kidney 70% and the Heart 30%. It guides the heat of Cinnamon Twig (Guizhi) and Aconite Root (Fuzi) to warm mostly in the Kidney and slightly outside the Heart. This ensures the Heart and Kidney Fires coexist harmoniously without contention, allowing Kidney Qi to connect with Heart Qi and Heart Qi to connect with Kidney Qi, enabling the Spleen and Stomach Qi to operate smoothly and ceaselessly. All this is due to the guiding merit of Chinese Yam. Did Master Zhang Zhongjing use it arbitrarily? ([Commentary] Bawei Wan tonifies the Fire of the Mingmen. When tonifying the Fire of the Mingmen, one worries that the Fire of the Pericardium will contend. Using Chinese Yam to resolve discord makes Heart and Kidney communicate, and Stomach and Spleen healthy. Not only is it unique, but the principle is so accurate; it is truly a profound herb of Master Zhang Zhongjing.)

Some suspect Chinese Yam should not be used in large doses. Why is there no harm in taking Liuwei Dihuang Wan for years? Could it be that it can be used in large doses when entering Dihuang Wan, but should be used in small doses when entering other formulas? One does not know that Chinese Yam can be used in large doses without taboo. What I previously said about avoiding it for those with strong Spleen was to worry about aiding Fire and stirring Dryness, not saying it cannot be used in large doses.

Some suspect Chinese Yam is slippery and moist, how can it stir Dryness? I reply: Chinese Yam generates Essence; naturally, it is not a substance that aids Dryness. When I say it aids Dryness, I mean it aids those who already have Fire, not those without Fire.

One asks: Chinese Yam is white in color, how can it darken beard hair? Why do I use it as the supreme herb for darkening beard hair? I reply: How can Chinese Yam darken beard hair? Chinese Yam enters the Kidney and particularly connects the Ren Mai (Conception Vessel) and Du Mai (Governing Vessel). The Ren and Du vessels ascend to the lips and cheeks. Therefore, borrowing Chinese Yam to be used within Black Sesame, Black Bean, Rehmannia Root (Shengdi Huang), Myrica Rubra Fruit (Nanzhu), and Polygonum Multiflorum Root (Heshouwu) guides the process to blacken the beard and temples. It is not that Chinese Yam itself turns black. One might ask again: If Chinese Yam is a guiding herb, it should not be heavily used as a sovereign drug. One does not know that although Chinese Yam does not change color, its nature and function truly greatly tonify Kidney Water. Those with insufficient Kidney Water absolutely cannot have black hair/temples. This is why I heavily use Chinese Yam to achieve efficacy.