五难曰∶脉有轻重，何谓也？
然∶初持脉如三菽之重，与皮毛相得者，肺部也。如六菽之重，
与血脉相得者，心部也。如九菽之重，与肌肉相得者，脾部也。如十
二菽之重，与筋平者，肝部也。按之至骨，举指来疾者，肾部也。故曰轻重也。
持脉，即按脉也。菽，豆之总名。肺位最高而主皮毛，故其脉如三菽之重。心在肺下主血脉，
故其脉如六菽之重。脾在心下主肌肉，故其脉如九菽之重。肝在脾之下主筋，故其脉如十二菽之
重。肾在肝下主骨，故其脉按之至骨，沉之至也，举指来疾，言其有力而急迫，即四难举指来实之
义也。此五脏本脉如此，倘有太过不及，则病脉也。
菽，豆之总名，诊脉轻重，何独取乎豆，且不言三菽、四菽、五菽，而必以三累加之，盖豆
在荚，累累相连，与脉动指下相类，以此意推之，言三菽重者，非三菽加于一部之上，乃一指下如
有一菽重也，通称三部，即三菽也。肺位高而主皮毛，故轻。六菽重者，三部各有二菽重也，心在
肺下主血脉，故稍重。九菽重者，三部各有三菽重也，脾在心下主肌肉，故又稍重。
十二菽重者，三部各有四菽重也，肝在脾下主筋，故较脾又加一菽重也。肾在肝下而主骨，故
其脉按之至骨，沉之至也，而举之来疾者何也？夫脉之体血也，其动者气也，肾统水火，火入水中
而化气，按之至骨，则脉气不能过于指下，微举其指，其来顿疾于前，此见肾气蒸动，勃不可遏，故曰
肾部也。举指两字，最宜索玩，不可忽也。若去此两字，是按之至骨而来转疾，乃牢伏类矣。
The Fifth Difficulty states: There is lightness and heaviness in pulse taking. What does this mean?
Answer: When initially grasping the pulse with a pressure equivalent to three beans (San Shu, total name for beans), where the sensation corresponds to the skin and hair (Pifū, integument), it is the Lung region. With a pressure equivalent to six beans, where the sensation corresponds to the blood vessels (Xuèguǎn, vascular system), it is the Heart region. With a pressure equivalent to nine beans, where the sensation corresponds to the muscles (Jīròu, muscular tissue), it is the Spleen region. With a pressure equivalent to twelve beans, where the sensation aligns with the sinews (Jīn, tendons and ligaments), it is the Liver region. Pressing down to the bone, and upon lifting the finger, the pulse returns swiftly and urgently, it is the Kidney region. Thus, it is referred to as lightness and heaviness.
"Grasping the pulse" refers to pressing on the pulse. "Shu" is the general term for beans. The Lung is located at the highest position and governs the skin and hair; therefore, its pulse feels like the weight of three beans. The Heart is below the Lung and governs the blood vessels; therefore, its pulse feels like the weight of six beans. The Spleen is below the Heart and governs the muscles; therefore, its pulse feels like the weight of nine beans. The Liver is below the Spleen and governs the sinews; therefore, its pulse feels like the weight of twelve beans. The Kidney is below the Liver and governs the bones; therefore, its pulse requires pressing down to the bone, which represents the extreme of deep palpation (Chén qǔ, deep pressure technique). Upon lifting the finger, the pulse comes back swiftly and urgently, indicating that the qi is powerful and urgent. This corresponds to the meaning of "lifting the finger reveals solidity" mentioned in the Fourth Difficulty. These are the normal pulses of the five Zang organs. If there is excess or deficiency, they become pathological pulses.
"Shu" is the general term for beans. Why is the bean chosen specifically to diagnose the lightness and heaviness of the pulse, and why are numbers like three, four, or five not mentioned individually, but rather accumulated starting from three? It is likely because beans grow in pods, connected one after another, resembling the pulsation felt under the fingers. Inferring from this intent, saying "three beans heavy" does not mean adding three beans onto one pulse position, but rather that under one finger, the sensation is equivalent to one bean's weight across the three positions (Sānbù, radial artery positions at Cun, Guan, and Chi), collectively termed "three beans." The Lung is high and governs the skin and hair, so the pressure is light. Six beans heavy means each of the three positions has a weight equivalent to two beans. The Heart is below the Lung and governs the blood vessels, so it is slightly heavier. Nine beans heavy means each of the three positions has a weight equivalent to three beans. The Spleen is below the Heart and governs the muscles, so it is slightly heavier again. Twelve beans heavy means each of the three positions has a weight equivalent to four beans. The Liver is below the Spleen and governs the sinews, so it is heavier than the Spleen by an additional bean's weight. The Kidney is below the Liver and governs the bones, so its pulse is pressed down to the bone, representing the extreme of deep palpation. Why then does it come back swiftly upon lifting? The substance of the pulse is blood, while its movement is driven by Qi. The Kidney controls both Water and Fire. When Fire enters Water, it transforms into Qi. When pressed down to the bone, the pulse Qi cannot manifest excessively under the fingers. Upon slightly lifting the finger, the pulse suddenly becomes more urgent than before. This reveals the steaming and activating power of Kidney Qi, vigorous and unstoppable, hence it is called the Kidney region. The phrase "lifting the finger" deserves careful contemplation and should not be ignored. If these two words were omitted, it would imply that the pulse becomes swift only when pressed to the bone, which would resemble a Firm (Láo) or Hidden (Fú) pulse.