The concept of position and form is the guiding principle of the main pulse. Position refers to the three regions and nine indicators. It may be at the inch, the foot, floating, or sinking. Number is used to record the quantity; numbers associated with slippery or rapid pulses are generally high, while those associated with slow or hesitant pulses are generally low. This includes conditions like fistula disease, bird pecking, shrimp swimming, and fish soaring, all of which fall under the category of number. As for form and momentum, they appear separately or together, each with its own profound meaning. A firm and steady pulse under the finger is the form, indicative of blood. A fluctuating and dynamic pulse under the finger is the momentum, indicative of qi. Neijing says: "The pulse is turbid and rapid, like a bubbling spring." It also says: "The pulse arrives like a newly kindled fire." Maijing says: "The pulse in the three regions is like boiling water in a pot, indicating that blood does not support qi, a unique manifestation of momentum." Neijing says: "The true liver pulse arrives like running a finger along a blade, sharp and cutting; the true heart pulse arrives like running a finger along coix seeds, clustered and knotted." This indicates that qi does not move blood, a unique manifestation of form. Therefore, when form and momentum appear separately, they are signs of a fatal pulse due to the extreme imbalance of qi and blood. In healthy individuals, qi and blood are always harmoniously blended, and form and momentum are in harmony. However, even a slight illness in qi or blood can lead to an imbalance in their harmony, which must be carefully discerned. For example, if the form is strong externally, the qi is fierce internally, indicating movement and largeness. If the qi is not very fierce, it is wiry or tight. If the qi is very deficient, it becomes thin or hollow, indicating a slight dominance of form over qi. If the form is weak externally, the qi is fierce internally, indicating a surging or slippery pulse. If the qi is not very fierce, it is soggy or weak. If the qi is very deficient, it becomes scattered or faint, indicating a slight dominance of qi over form.
Therefore, when diagnosing the pulse, place the finger on the pulse, first observe the form's thickness, thinness, hardness, and softness, then examine the arrival of qi. If it fills the vessel, slightly overflowing outside, expanding the pulse form, and fluctuating with deep and powerful movements without irregularity in arrival and departure, this indicates harmony between qi and blood. Why? The main pulse vessel is surrounded by countless fine vessels that distribute qi to the muscles, known as striae and interstice. If cold is excessive and yang qi cannot counter it, the fine vessels are first constricted by cold, and the pulse qi cannot overflow, resulting in a tight pulse. If the spleen and lung middle qi are insufficient and cannot fill the vessel, the pulse form may feel firm under the finger, but the qi arrives like a thread passing through the vessel, neither expanding nor fluctuating. This indicates a thick pulse form but thin pulse qi. If there is middle energizer phlegm-fluid retention, the turbid heat rises and steams the lungs, preventing lung qi from clearing and descending, causing the vessel to become tense. The pulse form feels firm under the finger, but the middle qi is blocked by phlegm-fluid retention and cannot flow smoothly, arriving like cotton under the finger, neither expanding nor fluctuating. This indicates a hard pulse form but soft pulse qi, not due to the vessel itself being hard, but because of turbid qi congestion, creating a stagnant qi within the moving vessel.Li Shi-cai, discussing the hollow pulse, said it feels like pressing on a scallion. When lightly pressed, it touches the upper skin; when moderately pressed, it reaches the hollow center; when deeply pressed, it touches the lower skin. This is not unique to the hollow pulse; vessels are inherently like this, but they vary in tightness, looseness, emptiness, and fullness. The hollow pulse is empty in the middle, making it more apparent. The hollow pulse is floating, only moving the upper skin, while the lower skin remains still. This indicates a thick pulse form but thin pulse qi. Momentum has arrival and departure, fluctuation; form has center and edges, top and bottom.
Therefore, in a healthy person, the harmony of the defensive and nutritive qi is balanced, and the flow of qi inside and outside the vessels corresponds in rhythm. Under the fingers, one does not feel the hard vessels or the arrival of qi, but rather senses that the main vessels are full, with a slight overflow to the sides. Moreover, the significance of the minute vessels is great. If the defensive qi sinks into the nutritive qi, causing a separation between the interior and exterior, the pulse under the fingers feels like a single raised line. This indicates that excessive fire is consuming body fluids, leading to the vessels becoming dry and blocked. This often results in dizziness, fainting, hemiplegia, and the risk of paralysis. In the past, Yu Chunshan once said that in elderly or weak individuals with prolonged illness nearing death, their organs feel like a single raised line, seemingly disconnected from the muscles. This is due to the failure of qi and blood to interact, and the separation of the defensive and nutritive qi, akin to an old tree withering, where the roots and side branches first show signs of decay, no longer receiving nourishment from the soil. This is the most subtle observation of physical form. As for assessing the pulse's condition, it is not only about observing the strength of its arrival and departure but also ensuring that between the arrival and departure, there is a continuous, smooth cycle, rising and falling gently, like a ring without abrupt breaks. There is a type of pulse that arrives with a sudden jerk and departs with a sudden jerk, with only four or five beats per breath, not exceeding the normal pulse rate. Yet, under the fingers, it feels abrupt, lacking the smooth, circular rhythm. This indicates a deficiency of body fluids and blood heat, with qi being dry and circulation impaired. Neijing refers to this as a "restless pulse." Thus, the summer pulse is likened to a hook because it arrives strong and departs weak, unable to form a complete circle; the hook represents a missing side of the circle. The restless pulse, however, arrives and departs uniformly, without any missing part, but it comes and goes abruptly, not in a circular motion but in a straight, broken line. This is what Bian Que referred to as a "jumping pulse." Neijing also states that when the pulse moves, the yang qi arrives first, and the yin qi follows. This further distinguishes the subtle dynamics of yin and yang at the moment the pulse begins to move. Hence, Nan Jing discusses the condition where the pulse is large in the front and small in the back, leading to headache and dizziness; or small in the front and large in the back, causing chest fullness and shortness of breath. Zhang Zhongjing mentioned that when the pulse is small at the beginning and large at the root, the disease is in the exterior. Later scholars differentiated that a strong pulse before movement indicates excess qi, while a weak pulse indicates deficiency; a strong pulse after movement indicates excess blood, while a weak pulse indicates deficiency. These are all subtle analyses, representing the highest level of pulse study and the wisdom of diagnostic practice.