Taken from ‘Classical Clinical Insights from the Fire Spirit Current’ by Zhang Cun’ti [张存悌, 经典火神派临床心悟]

Yang qi is divided into upper, middle, and lower parts. The upper burner contains the Yang of the heart and lungs, the middle burner contains the Yang of the spleen and stomach, and the lower burner contains the Yang of the liver and kidneys. “The lower Yang is the root of the Yang of the upper and middle burners,” signifies that the Kidney Yang in the lower burner is the root of Yang qi in the upper and middle burners. In other words, among all types of Yang qi, Zheng Qin’an particularly emphasized the role of Kidney Yang. “A person’s life and destiny rely entirely on the single Yang [line] in the Kan hexagram,” indicating that Kidney Yang is the fundamental source of Yang qi in the human body and the root of life and destiny. This also forms the theoretical basis for his advocacy of using Fuzi and Sini-type prescriptions to warm and support Kidney Yang.

圖友人黄某，乙酉九月患腹痛，每食甜物少愈。医者以为燥也，用甘润之药不效。旋用下药，痛益甚。延子诊视，六脉细小，喜按，口淡，倦怠，断为寒证。投以理中汤加木香，旋止旋发，夜间更甚。予曰：“夜为阴，阴寒盛，夜间痛更甚也。”用通脉四逆汤加白芍，十余服痊愈。（易巨荪治案）

A friend named Mr. Huang suffered from abdominal pain in the ninth month of the Yiyou year. The pain lessened whenever he ate sweet foods. Doctors believed it to be dryness and used sweet and moistening medicines to no avail. Subsequently, they used purgative medicines, which worsened the pain. Upon examination, all six of his pulses were thin and small, he liked pressure on the abdomen, had a bland taste in his mouth, and felt fatigued. I diagnosed it as a cold condition. I prescribed Lizhong Tang with added Mu Xiang, which provided temporary relief but the pain recurred, especially at night. I said, “Night is Yin time, and Yin cold is prevalent, hence the pain worsens at night.” I then used Tongmai Sini Tang with added Baishao, and after more than ten doses, he fully recovered. (Case of Yi Jusun)

张存悌按（以下简称张按）：此案腹痛，先从中阳论治，“投以理中汤加木香，旋止旋发”。以“夜为阴，阴寒盛，夜间痛更甚”为辨证眼目，专力扶肾阳，用通脉四逆汤加白芍而愈，值得揣摩。

Commentary by Zhang Cunti

In this case of abdominal pain, the initial treatment focused on the Yang of the middle burner with “Lizhong Tang plus Mu Xiang,” which provided temporary relief. The key to the differentiating [factor of the] pattern was that “night is Yin, and Yin cold is prevalent at night, hence the pain worsens at night,” leading to the decision to specifically support Kidney Yang using Tongmai Sini Tang with added Baishao, resulting in the resolution [of the condition]. This approach is worth pondering.