肉桂∶味辛而甘，气香而窜，性大热纯阳。为其为树身近下之皮，故性能下达，暖丹田，壮元阳，补相
火。其色紫赤，又善补助君火，温通血脉，治周身血脉因寒而痹，故治关节腰肢疼痛及疮家白疽。木得桂则枯，
且又味辛属金，故善平肝木，治肝气
横恣多怒，若肝有热者，可以龙胆草、芍药诸药佐之。《神农本草经》谓其为诸药之先聘通使，盖因其香窜之
气内而脏腑筋骨，外而经络腠理，倏忽之间莫不周遍，故诸药不能透达之处，有肉桂引之，则莫不透达也。
按∶附子、肉桂，皆气味辛热，能补助元阳，然至元阳将绝，或浮越脱陷之时，则宜用附子而不宜用肉桂。
诚以附子但味浓，肉桂则气味俱浓，补益之中实兼有走散之力，非救危抉颠之大药，观仲景《伤寒论》少阴诸
方，用附子而不用肉桂可知也。
肉桂气味俱浓，最忌久煎。而坊间又多捣为细末，数沸之后，药力即减，况煎至数十沸乎。至于石膏气味
俱淡，且系石质，非捣细煎之，则药力不出，而坊间又多不为捣细。是以愚用石膏，必捣为细末然后煎之。若
用肉桂，但去其粗皮，而以整块入煎。至药之类肉桂、类石膏者，可以肉桂、石膏为例矣。
肉桂味辣而兼甜，以甜胜于辣者为佳，辣胜于甜者次之。然约皆从生旺树上取下之皮，故均含有油性，
皆可入药，至其薄浓不必计也。若其味不但不甚甜，且不甚辣，又兼甚干枯者，是系枯树之皮，不可用也。
肉桂：味道辛甘，气味芳香且善于走窜，药性大热，属于纯阳之品。因为它是生长在树干靠近根部的树皮，所以其性能能够下行，温暖丹田，壮旺元阳，补益相火（肾中命门之火）。它的颜色紫赤，又善于补助君火（心火），温通血脉，治疗因寒邪导致周身血脉痹阻不通，因此能治疗关节、腰肢疼痛以及疮疡患者出现的白疽（一种阴寒性质的疮疡）。树木遇到桂枝就会枯萎，加上它味辛属金，所以善于平抑肝木，治疗肝气横逆、易怒的症状；如果肝脏有热，可以配合龙胆草、芍药等药物来佐制。《神农本草经》称它为各种药物的先导使者，大概是因为它芳香走窜的气机，内至脏腑筋骨，外达经络腠理，瞬间便能周遍全身，所以在其他药物无法透达的地方，若有肉桂引导，就没有不能透达的。
按语：附子和肉桂，都是气味辛热的药物，都能补助元阳。然而到了元阳即将衰竭，或者浮越脱陷的时候，就应当使用附子而不宜使用肉桂。确实因为附子只是气味浓厚，而肉桂则是气味都极其浓厚，在补益之中实际上兼有走散的力量，并不是挽救危急、力挽狂澜的大药，观察张仲景《伤寒论》中少阴病的各个方剂，使用附子而不用肉桂，就可以知道这一点。
肉桂气味都非常浓厚，最忌讳长时间煎煮。而市面上又多将其捣成细末，经过几次煮沸后，药效就会减少，何况是煎煮几十次呢？至于石膏，气味都很淡，而且属于石质药材，如果不捣碎煎煮，药效就无法析出，而市面上又多不将其捣碎。所以我使用石膏时，一定要捣成细末然后煎煮。如果使用肉桂，只需去掉粗皮，以整块形式放入煎煮。其他类似肉桂或石膏特性的药材，都可以参照肉桂和石膏的处理方法来处理。
肉桂味道辛辣并带有甜味，以甜味胜过辣味的为佳，辣味胜过甜味的稍次。但大约都是从生长旺盛的树上剥下的树皮，所以都含有油性，都可以入药，不必计较其厚薄。如果它的味道不仅不太甜，也不太辣，而且非常干枯，这是枯树的树皮，不可使用。
Cinnamon Bark (Rougui): It has a pungent and sweet taste, an aromatic odor that is penetrating and dispersing, and a very hot nature, belonging to pure Yang. Since it is the bark from the lower part of the tree trunk near the roots, its action tends to descend, warming the Dantian (lower abdomen/Energy center), strengthening the Primordial Yang, and supplementing the Ministerial Fire (Fire of the Mingmen in the Kidneys). Its purple-red color enables it to assist the Sovereign Fire (Heart Fire), warm and unblock the blood vessels, and treat bi-syndrome (obstruction causing pain) of the whole body's blood vessels due to cold. Therefore, it treats pain in joints, waist, and limbs, as well as Baiju (a type of yin-cold abscess) in patients with sores. Wood withers when encountering Cinnamon Twig; furthermore, since its pungent taste corresponds to Metal, it is good at pacifying Liver Wood, treating excessive anger caused by rebellious Liver Qi. If there is heat in the Liver, it can be assisted by herbs such as Gentian Root (Longdancao) and White Peony Root (Shaoyao). The *Shennong Bencao Jing* states that it acts as the vanguard messenger for various medicines, likely because its aromatic and penetrating qi reaches internally to the zang-fu organs, tendons, and bones, and externally to the meridians and interstices, pervading the entire body in an instant. Thus, in places where other medicines cannot penetrate, with the guidance of Cinnamon Bark, nothing remains unpenetrated.
Note: Aconite Root (Fuzi) and Cinnamon Bark (Rougui) both have pungent and hot flavors and odors, capable of supplementing the Primordial Yang. However, when the Primordial Yang is on the verge of exhaustion or floating away into collapse, Aconite Root should be used rather than Cinnamon Bark. This is indeed because Aconite Root has only a strong flavor, whereas Cinnamon Bark has both strong flavor and odor; within its tonifying action, it actually possesses dispersing power. It is not a major medicine for rescuing critical conditions and reversing dire situations. Observing the formulas for Shaoyin disease (Lesser Yin Disease) in Zhang Zhongjing's *Treatise on Cold Damage Diseases* (*Shanghan Lun*), which use Aconite Root but not Cinnamon Bark, confirms this.
Cinnamon Bark has extremely strong flavor and odor, and long decoction is strictly contraindicated. In the market, it is often ground into fine powder; after just a few boils, its medicinal power diminishes, let alone boiling for dozens of times. Conversely, Gypsum Fibrosum (Shigao) has very faint flavor and odor, and being a mineral substance, its medicinal power will not be released unless it is ground fine and decocted. However, in the market, it is often not ground fine. Therefore, when I use Gypsum Fibrosum, I must grind it into fine powder before decocting. When using Cinnamon Bark, one should merely remove the rough bark and add the whole piece to the decoction. Other materials similar to Cinnamon Bark or Gypsum Fibrosum can follow these examples.
Cinnamon Bark tastes spicy and sweet; those where sweetness surpasses spiciness are superior, while those where spiciness surpasses sweetness are inferior. Generally, they are all barks taken from vigorously growing trees, thus containing oiliness, making them suitable for medicinal use, regardless of thickness. If the taste is neither particularly sweet nor spicy, and the bark is very dry and withered, it is bark from a dead tree and should not be used.