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The clinical manifestations of exterior contraction (Wai Gan) and interior injury (Nei Shang) are similar, yet their treatment principles are vastly different; thus, they must be carefully distinguished. Injury caused by improper diet, overexertion, and the seven emotions and six desires constitutes interior injury; injury caused by wind, cold, summer-heat, and dampness constitutes exterior contraction.

Fever due to interior injury is intermittent, appearing and disappearing; fever due to exterior contraction is high-grade and continuous without cessation. Chills (E Han) due to interior injury resolve upon warming; chills due to exterior contraction persist even with thick clothing and proximity to fire. Wind aversion (E Feng) due to interior injury does not fear strong winds but rather fears drafts from cracks; wind aversion due to exterior contraction causes aversion upon merely seeing wind. Headache due to interior injury comes and goes; headache due to exterior contraction is continuous and unceasing until the exterior pathogenic factor transmits inward.

Interior injury accompanied by dampness may present without thirst, or if heart fire invades the lung metal, it may present with dry thirst; exterior contraction requires two to three days for the exterior heat to transmit inward before thirst arises. Interior injury leads to heat damaging qi, resulting in heavy, fatigued limbs, weakness, and a desire to lie down; exterior contraction involves wind damaging sinews and cold damaging bones, causing pain throughout the body's sinews and bones. Interior injury leads to shortness of breath and insufficient respiration. Exterior contraction presents with panting, qi congestion, and excessiveness. Interior injury manifests as heat in the palms; exterior contraction manifests as heat on the dorsum of the hands. Heaven's qi connects with the lungs; the nose is the external manifestation of the lungs; exterior contraction of cold damage results in nasal congestion, while wind damage results in runny nose.

If one can eat and drink normally, taste food properly, feel harmony in the abdomen, and have normal urination and defecation, this indicates Earth's qi connecting with the spleen; the mouth is the external manifestation of the spleen. Interior injury results in reluctance to speak, aversion to eating, loss of taste, yellow-red urine, and either constipation or loose stools. The Renying pulse at the left neck primarily governs exterior syndromes. In exterior contraction, the Renying pulse is larger than the Qikou pulse; the Qikou pulse at the right wrist primarily governs interior syndromes. In interior injury, the Qikou pulse is larger than the Renying pulse.

Interior injury syndromes belong to deficiency, requiring warming, tonifying, and harmonizing methods; exterior contraction syndromes belong to excess, requiring diaphoretic, emetic, and purgative methods. If interior injury symptoms are mistaken for exterior contraction and treated with reckless sweating to release the exterior, vital qi will be further depleted, leading to disaster swiftly. Therefore, Buzhong Yiqi Tang (Tonify the Middle and Augment the Qi Decoction) is established as the primary formula. There are also cases where interior injury and exterior contraction coexist. If interior injury is severe, tonification and nourishment should take precedence; if exterior contraction is severe, dispersing and releasing the exterior is urgent. This decoction (Buzhong Yiqi Tang) is not suitable for patients with phlegm and vomiting in the upper jiao, damp-heat in the middle jiao, or food stagnation causing fullness in the chest/diaphragm.

The pulse of interior injury: the Cun and Guan positions on the right hand are necessarily large, but initially appearing slippery, they become soft and forceless upon prolonged pressing; the left pulse is peaceful and not rapid, though sometimes weak, just smaller than the right hand pulse. This is a pulse of weak qi and flourishing fire; rapidity and largeness indicate deficient fire, while forcelessness indicates weak qi. Mistaking this for excess fire and recklessly using cold-cooling herbs will further injure middle qi, causing the fire to intensify. Some may mistake the tight and vigorous Qikou pulse for food stagnation. However, the distinction between forceful and forceless pulses is already clear. Moreover, those with retained food stagnation must experience nausea, fullness, and hyperactive spirit without fatigue. Those with interior injury must not experience epigastric stuffiness or fullness, but rather fatigue, weakness, and reluctance to speak, which serves as further verification.