体象 虚合四形，浮大迟软；及乎寻按，几不可见。
虚之为义，中空不足之象，专以软而无力得名者也。
主病 虚主血虚，又主伤暑。左寸虚者，心亏惊悸。虚在左关，血不营筋。左尺得虚，腰膝痿痹。
右寸虚者，自汗喘促。虚在右关，脾寒食滞。右尺得虚，寒证蜂起。
《脉经》曰∶“血虚脉虚。”而独不言气虚者何也？气为阳，主浮分，血为阴，主沉分。今浮分大而沉分空，故
独主血虚耳。若夫肺脉见之，又主气怯者，肺与干天合德，不浮而沉，气分欲竭之兆也。血少则不足以
济心主高拱之权，而动见章皇。肝为血海而主筋，虚则筋失其养。腰者，肾之府也；膝者，骨之屈申开阖
处也；虚则不为我用。阳气虚则不能卫外而自汗；真气虚而喘促者，盖由机缄不相接续。食滞者脾胃
虚寒，干健坤顺，两失其职。真火衰而诸证毕集，非转阳和之令，事何克济乎！
虚脉又主伤暑者，盖暑为阳邪，其势足以烁石流金，干于脾则吐利，干于心则烦心，并于上则头重，并
于下则便秘；其见于脉也，不洪数而反见虚者，因暑性炎热，使人表气易泄，故脉必虚耳。
按《脉经》曰∶“迟大而软，按之豁豁然空。”此言最为合义。虽不言浮字，而曰按之豁然空，则浮字之义
已包含矣。崔紫虚以为形大力薄，其虚可知，但欠迟字之义耳。伪诀云∶“寻之不足，举之有余。”是浮脉
而非虚脉矣。浮以有力得名，虚以无力取象，有余二字。安可施之虚脉乎？杨仁斋曰∶“状为柳絮，散漫
而迟。”滑伯仁曰∶“散大而软。”二家之言，俱是散脉而非虚脉矣。夫虚脉按之虽软，犹可见也；散脉按
之绝无，不可见也。虚之异于濡者，虚则迟大而无力，濡则细小而无力也。虚之异于芤者，虚则愈按而
愈软，芤则重按而仍见也。夫虚脉兼迟，迟为寒象，大凡证之虚极者必挟寒，理势然也。故虚脉行于指
下，则益火之原，以消阴翳。更有浮取之而且大且数，重按之而豁然如无，此名内真寒而外假热，古人
以附子理中汤冰冷与服，治以内真热而外假寒之剂也。
[Physical Manifestation]
The Xu (Deficiency) pulse exhibits four characteristics: it is superficial (Floating), large, slow, and soft upon light palpation; however, upon deep pressure (Searching and Pressing), the pulse is barely visible or palpable.
The meaning of the Xu pulse refers to the image of a hollow vessel with insufficient Qi and Blood, named specifically for its softness and lack of force.
[Associated Diseases]
The Xu pulse primarily indicates Blood Deficiency and also Summerheat Injury.
A Xu pulse at the Left Cun position indicates Heart deficiency, leading to fright and palpitations.
A Xu pulse at the Left Guan position indicates that Blood fails to nourish the tendons.
A Xu pulse at the Left Chi position indicates flaccidity and bi-syndrome in the lower back and knees.
A Xu pulse at the Right Cun position indicates spontaneous sweating and panting/shortness of breath.
A Xu pulse at the Right Guan position indicates Spleen-Stomach cold and food stagnation.
A Xu pulse at the Right Chi position indicates that various Cold syndromes arise in succession.
The *Mai Jing* (Pulse Classic) states: "Blood deficiency results in a Deficient pulse." But why does it not mention Qi deficiency? This is because Qi belongs to Yang and manifests primarily in the superficial layer (light pressure); Blood belongs to Yin and manifests primarily in the deep layer (heavy pressure). Since the superficial layer appears large while the deep layer appears empty, the Xu pulse alone indicates Blood deficiency. However, if this pulse appears in the Lung position, it also indicates Qi timidity. The Lung harmonizes with Heaven, and its virtue is descending; if the pulse is not superficial but deep, it is a sign that Qi is about to be exhausted. When Blood is scant, it cannot support the Heart's dominant authority, leading to restlessness and confusion. The Liver is the Sea of Blood and governs the tendons; when deficient, the tendons lose their nourishment. The waist is the mansion of the Kidney; the knee is the place where bones flex and extend; when deficient, these parts cannot function properly. When Yang Qi is deficient, it cannot protect the exterior, leading to spontaneous sweating; when True Qi is deficient, causing panting, it is due to the failure of the mechanism to connect continuously. Food stagnation occurs due to Spleen-Stomach deficiency-cold, where both the Spleen's transformation and the Stomach's descending functions fail. When the True Fire (Mingmen Fire) declines, all symptoms gather; unless the command of Yang and harmony is restored, how can success be achieved?
The Xu pulse also indicates Summerheat Injury because Summerheat is a Yang pathogen, powerful enough to melt stone and flow metal. If it affects the Spleen, it causes vomiting and diarrhea; if it affects the Heart, it causes vexation; if it moves upward, it causes heavy head; if it moves downward, it causes constipation. In terms of pulse manifestation, instead of being surging and rapid, it appears deficient because the nature of Summerheat is hot, causing the exterior Qi to leak easily, thus the pulse must be deficient.
According to the *Mai Jing*: "Slow, large, and soft, pressing reveals an empty feeling." This statement is most accurate. Although it does not explicitly mention "superficial," saying "pressing reveals emptiness" implies the superficial nature. Cui Zixu believed that a large form with weak force indicates deficiency, which is clear, but it lacks the meaning of "slow." The false rhyme says: "Insufficient when searching, abundant when lifting." This describes a Floating pulse, not a Xu pulse. The Floating pulse is defined by strength, while the Xu pulse is defined by weakness; how can "abundant" apply to a Xu pulse? Yang Renzhai said: "Resembling willow catkins, scattered and slow." Hua Borin said: "Scattered, large, and soft." Both descriptions refer to the San (Scattered) pulse, not the Xu pulse. The difference between the Xu pulse and the San pulse is that although the Xu pulse is soft upon pressing, it is still visible; the San pulse is completely absent upon pressing and invisible. The difference between the Xu pulse and the Ru (Soggy) pulse is that the Xu pulse is slow, large, and forceless, whereas the Ru pulse is fine, small, and forceless. The difference between the Xu pulse and the Kou (Hollow) pulse is that the Xu pulse becomes softer the deeper one presses, whereas the Kou pulse remains palpable even with heavy pressure. The Xu pulse combines with slowness; slowness is a sign of Cold. Generally, extreme deficiency conditions must involve Cold, which is logical and natural. Therefore, when the Xu pulse appears under the fingers, one should tonify the source of Fire to eliminate Yin shadows. Furthermore, if the pulse is large and rapid upon light palpation but feels empty like nothing upon heavy palpation, this is called "True Cold inside and False Heat outside." Ancient practitioners used Fuzi Lizhong Tang (Aconite Decoction for Regulating the Middle), typically a formula for treating "True Heat inside and False Cold outside," administered coldly (or as per specific ancient protocols, though logically contradictory in standard theory).