二十难曰∶经言脉有伏匿。伏匿于何脏而言伏匿邪？然∶谓阴阳更相乘、更相伏也。脉居阴部而反阳
脉见者，为阳乘阴也，脉虽时沉涩而短，此谓阳中伏阴也；脉居阳部而反阴脉见者，为阴乘阳也，脉虽时浮
滑而长，此谓阴中伏阳也。
重阳者狂，重阴者癫。脱阳者见鬼，脱阴者目盲。
二十一难曰∶经言人形病、脉不病曰生，脉病、形不病曰死，何谓也？然∶人形病、脉不病，非有
不病者也，谓息数不应脉数也，此大法。
二十二难曰∶经言脉有是动，有所生病。一脉变为二病者，何也？然∶经言是动者，气也；所生病者，
血也。邪在气，气为是动∶邪在血，血为所生病，气主 之。血主濡之。气留而不行者，为气先病也；血
壅而不濡者。为血后病也。故先为是动，后所生也。
二十三难曰∶手足三阴三阳，脉之度数，可晓以不？然∶手三阳之脉，从手至头，长五尺，五六合三
丈。手三阴之脉，从手至胸中，长三尺五寸，三六一丈八尺，五六三尺，合二丈一尺。足三阳之脉，
从足至头，长八尺，六八四丈八尺。足三阴之脉，从足至胸，长六尺五寸，六六三丈六尺，五六三尺，
合三丈九尺。人两足跷脉，从足至目，长七尺五寸，二七一丈四尺，二五一尺，合一丈五尺。督脉、
任脉各长四尺五寸，二四八尺，二五一尺，合九尺。凡脉长一十六丈二尺，此所谓十二经脉长短之数
也。
经脉十二，络脉十五，何始何穷也？然∶经脉者，行血气，通阴阳，以荣于身者也。其始从中焦，
注手太阴、阳明；阳明注足阳明、太阴；太阴注手少阴、太阳；太阳注足太阳、少阴；少阴注手心主、
少阳；少阳注足少阳、厥阴；厥阴复还注手太阴。别络十五，皆因其原，如环无端，转相灌溉，朝于
寸口、人迎，以处百病，而决死生也。
经云∶明知终始，阴阳定矣。何谓也？然∶终始者，脉之纪也。寸口、人迎，阴阳之气，通于
朝使，如环无端，故曰始也。终者，三阴三阳之脉绝，绝则死。死各有形，故曰终也。
第二十难说：医经上说脉象有伏匿的现象。所谓伏匿，是指在哪一脏而言的呢？回答说：是指阴阳相互乘袭、相互潜伏的关系。如果脉象出现在阴部（尺部），却反而出现阳脉（如浮、大、数等），这是阳邪乘袭阴位，虽然脉象有时表现为沉、涩、短，这叫做“阳中伏阴”；如果脉象出现在阳部（寸部），却反而出现阴脉（如沉、细、迟等），这是阴邪乘袭阳位，虽然脉象有时表现为浮、滑、长，这叫做“阴中伏阳”。
阳气重盛的人会发生狂证，阴气重盛的人会发生癫证。阳气脱失的人会看见鬼怪（幻觉），阴气脱失的人会双目失明。
第二十一难说：医经上说，人形体有病而脉象无病的是可生，脉象有病而形体无病的是必死，这是什么意思呢？回答说：人形体有病而脉象无病，并不是指真的没有病，而是指呼吸次数与脉搏跳动次数不相适应（即脉症不符），这是判断生死的大法。
第二十二难说：医经上说脉象有“是动”和“所生病”两种情况。为什么一脉可以变为两种病呢？回答说：医经上说，“是动”病属于气分病变；“所生病”属于血分病变。邪气在气分，气机逆乱导致“是动”病；邪气在血分，血液运行失常导致“所生病”。气主要推动温煦身体，血主要濡养滋润身体。气停留而不能正常运行，是气先发生病变；血液壅滞而不能濡养，是血后发生病变。所以先出现“是动”病，后出现“所生病”。
第二十三难说：手足三阴三阳经脉的长度度数，可以讲清楚吗？回答说：手三阳经的脉，从手走到头，长度五尺，六条合计三尺丈。手三阴经的脉，从手走到胸中，长度三尺五寸，三条合计一丈八尺，加上五六三尺，总共二丈一尺。足三阳经的脉，从脚走到头，长度八尺，六条合计四丈八尺。足三阴经的脉，从脚走到胸，长度六尺五寸，六条合计三丈六尺，加上五六三尺，总共三丈九尺。人的两条跷脉（此处指阴跷、阳跷），从脚走到眼睛，长度七尺五寸，两条合计一丈四尺，加上二五一尺，总共一丈五尺。督脉、任脉各长四尺五寸，两条合计八尺，加上二五一尺，总共九尺。所有经脉总长度为一十六丈二尺，这就是所说的十二经脉长短的度数。
十二经脉和十五络脉，从哪里开始，到哪里终结呢？回答说：经脉，是运行气血，沟通阴阳，以营养全身的通道。它们起始于中焦，注入手太阴肺经、手阳明大肠经；手阳明大肠经注入足阳明胃经、足太阴脾经；足太阴脾经注入手少阴心经、手太阳小肠经；手太阳小肠经注入足太阳膀胱经、足少阴肾经；足少阴肾经注入手厥阴心包经、手少阳三焦经；手少阳三焦经注入足少阳胆经、足厥阴肝经；足厥阴肝经又返还注入手太阴肺经。十五别络，都源于各自的原穴，像圆环一样没有端点，互相转注灌溉，汇聚于寸口和人迎穴，以此来诊治各种疾病，并决断生死。
医经说：明白了终始的道理，阴阳就能确定了。这是什么意思呢？回答说：终始，是脉气的纲纪。寸口和人迎两处，阴阳之气相通，如同朝使往来，像圆环一样没有端点，所以称为“始”。所谓“终”，是指三阴三阳的经脉之气断绝，断绝就会死亡。死亡各有其形态表现，所以称为“终”。
Difficulty 20 states: The classic texts mention that pulses may be "hidden" (Fu Ni). Regarding which zang organ is this hiddenness discussed? The answer is: it refers to the mutual overcoming and hiding of yin and yang. When a pulse appears in the yin position (cun chi, specifically chi) but reveals yang characteristics (such as floating, large, or rapid), this is described as "yang overcoming yin." Although the pulse may occasionally present as deep, choppy, and short, this is termed "yin hidden within yang." Conversely, when a pulse appears in the yang position (cun chi, specifically cun) but reveals yin characteristics (such as deep, fine, or slow), this is described as "yin overcoming yang." Although the pulse may occasionally present as floating, slippery, and long, this is termed "yang hidden within yin."
Excess of yang leads to mania (Kuang); excess of yin leads to depression/epilepsy (Dian). Loss of yang results in hallucinations (seeing ghosts); loss of yin results in blindness.
Difficulty 21 states: The classic texts say that if the body shows signs of disease but the pulse does not, the prognosis is survival; if the pulse shows signs of disease but the body does not, the prognosis is death. What does this mean? The answer is: "Body diseased, pulse healthy" does not mean there is absolutely no disease. It refers to a discrepancy between the respiratory rate and the pulse rate. This is a general principle for determining life and death.
Difficulty 22 states: The classic texts mention that pulses involve both "Shi Dong" (Is Moving) and "Suo Sheng Bing" (So-Called Generated Diseases). Why can one meridian manifest as two types of disease? The answer is: The classics state that "Shi Dong" relates to Qi disorders, while "Suo Sheng Bing" relates to Blood disorders. When pathogenic factors are in the Qi level, Qi disturbance causes "Shi Dong"; when pathogenic factors are in the Blood level, Blood stasis causes "Suo Sheng Bing." Qi primarily moves and warms the body, while Blood primarily moistens and nourishes it. When Qi stagnates and fails to circulate, it is a primary Qi disorder; when Blood becomes obstructed and fails to nourish, it is a secondary Blood disorder. Therefore, "Shi Dong" occurs first, followed by "Suo Sheng Bing."
Difficulty 23 asks: Can the lengths and measurements of the twelve meridians of the hand and foot, yin and yang, be explained? The answer is: The three yang meridians of the hand run from the hand to the head, each measuring five chi. Six times five equals three zhang. The three yin meridians of the hand run from the hand to the chest, each measuring three chi and five cun. Three times six yields one zhang and eight chi; adding five times six (three chi) results in a total of two zhang and one chi. The three yang meridians of the foot run from the foot to the head, each measuring eight chi. Six times eight yields four zhang and eight chi. The three yin meridians of the foot run from the foot to the chest, each measuring six chi and five cun. Six times six yields three zhang and six chi; adding five times six (three chi) results in a total of three zhang and nine chi. The two Qiao meridians (Yin and Yang Qiao) run from the foot to the eyes, each measuring seven chi and five cun. Two times seven yields one zhang and four chi; adding two times five (one chi) results in a total of one zhang and five chi. The Du Mai (Governing Vessel) and Ren Mai (Conception Vessel) each measure four chi and five cun. Two times four yields eight chi; adding two times five (one chi) results in a total of nine chi. The total length of all these vessels is sixteen zhang and two chi. This constitutes the measurement of the twelve main meridians.
There are twelve main meridians and fifteen collaterals. Where do they begin and where do they end? The answer is: The meridians transport Qi and Blood, connect yin and yang, and nourish the body. They originate at the Middle Jiao (Middle Burner), flowing into the Hand Taiyin Lung Meridian and Hand Yangming Large Intestine Meridian; the Hand Yangming flows into the Foot Yangming Stomach Meridian and Foot Taiyin Spleen Meridian; the Foot Taiyin flows into the Hand Shaoyin Heart Meridian and Hand Taiyang Small Intestine Meridian; the Hand Taiyang flows into the Foot Taiyang Bladder Meridian and Foot Shaoyin Kidney Meridian; the Foot Shaoyin flows into the Hand Jueyin Pericardium Meridian and Hand Shaoyang Sanjiao Meridian; the Hand Shaoyang flows into the Foot Shaoyang Gallbladder Meridian and Foot Jueyin Liver Meridian; the Foot Jueyin returns to flow into the Hand Taiyin Lung Meridian. The fifteen collateral vessels all arise from their respective Yuan-Source points, forming a continuous circle without beginning or end, irrigating each other, and converging at the Cun Kou (Radial Artery) and Ren Ying (Carotid Artery) to diagnose various diseases and determine life and death.
The classics state: "If one clearly understands the beginning and end, yin and yang can be determined." What does this mean? The answer is: "Beginning and End" refers to the cycle of pulse Qi. The Cun Kou and Ren Ying represent the connection of yin and yang Qi, circulating like messors to the court, forming a circle without end; thus, this is called the "Beginning." The "End" refers to the cessation of Qi in the three yin and three yang meridians. Cessation leads to death. Death presents with specific forms, thus it is called the "End."