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The onset is regular with intervals, resembling the tide's ebb and flow, occurring punctually once a day. (Febrile sensation belongs to Fire pathogen. The meridian affected by Fire pathogen will manifest symptoms when its Qi is at its peak; for instance, Heart Meridian heat manifests as tidal fever at Wu hour, Kidney Meridian heat at Zi hour, etc., as detailed in the chapter on Fever.) If it occurs three to five times a day, it is merely ordinary fever, not termed tidal fever. Tidal fever can be either deficiency or excess type. In Shanghan disease, afternoon tidal fever (occurring between 3-5 PM) indicates Stomach excess heat, which is detailed in *Shanghan Lun*. For other conditions causing tidal fever: if accompanied by dry and constipated stool, scanty dark urine, preference for cold drinks, aversion to heat, and restless sleep, this indicates Qi excess; treat with Shen Su Yin (see Fever chapter) or Xiao Chai Hu Tang (see Cold and Heat chapter). If characterized by Qi deficiency, poor appetite, mental fatigue, and emaciation, where although symptoms temporarily subside, there remains residual heat in the five centers (palms, soles, and chest), this is deficiency type; treat with Fu Ling Bu Xin Tang, Shi Quan Da Bu Tang, or Yang Rong Tang (these two formulas are listed in the Deficiency Damage chapter). For post-illness lack of regulation, use Ba Zhen San. Symptoms resembling deficiency but accompanied by chest and diaphragm fullness/stuffiness, back pain, and ineffectiveness of tonifying herbs indicate Phlegm-Fluid retention. Phlegm-fluid moves with Qi, so heat also tides with fluid; treat with Wu Yin Tang. Slight night fever where the patient is unaware, normal activity upon waking, normal diet, and no other suspicious symptoms indicate Blood deficiency, where Yin fails to balance Yang; moisten and tonify using formulas like Fu Ling Bu Xin Tang mentioned above. Slippery pulse with retained food and evening fever should be sought in the Food Retention chapter. Blood deficiency causing five-center heat worsening at night is treated with Si Wu Er Lian Tang. After recovery from febrile disease, if residual heat lingers in meridians causing recurrent fever, and urination is clear and free, it is due to misusing cold-natured herbs leading to Middle Qi deficiency and cold, failing to expel pathogens; use large doses of Ginseng and Atractylodes Macrocephala Rhizome to tonify, resolving via chills-and-sweating; add Angelica Sinensis Root and Rehmannia Glutinosa Root if Blood deficiency exists.

(Light cases involve fearfulness; severe cases involve shivering.)
Aversion to cold is divided into internal injury and external contraction.

1. Initial External Contraction
Wind-strike involves aversion to wind; Cold-strike involves aversion to cold, similar to alcohol injury involving aversion to wine or food injury involving aversion to food. This is because exterior Yang is constrained by pathogens, seeking warmth to unblock and circulate. Thus, the obstruction causing aversion to cold persists before fever onset and continues during fever; patients do not wish to remove covers, and may feel chilly even near fire or in summer, experiencing fear regardless of wind presence. (Aversion to cold differs slightly from aversion to wind; aversion to wind occurs only with wind, whereas aversion to cold occurs with or without wind.) It ceases only after the exterior syndrome resolves. Symptoms must include fever, anhidrosis, stiff neck and occiput, and floating-tight pulse. (This is what is meant by "fever with aversion to cold originates from Yang.") If there is no fever but aversion to wind and curling up while lying down, it indicates direct transmission to Yin meridians. (This is what is meant by "no fever with aversion to cold originates from Yin." According to *Shanghan Lun*, Shaoyin and Jueyin chapters mention aversion to cold, but Taiyin does not, likely due to missing text. In fact, all six meridians can present aversion to cold; arbitrary distinction is incorrect.)

2. Deep Penetration of Yang Pathogens in Shanghan
Transmitted Yang pathogens penetrate deeply into Yin levels, causing heat to stagnate internally and exterior Qi to be blocked. Limbs become cold and inverted, with aversion to cold, mimicking Yin syndromes. This is the case where "aversion to cold is not true cold, but clearly a heat syndrome."

3. Resolution Phase of Shanghan
According to *Shanghan Lun · Bian Mai Pian*: "Floating and tight pulse, hollow upon pressure, indicates inherent deficiency, thus chills and sweating should occur." Since the person is inherently deficient, chills occur; due to floating pulse, sweating leads to resolution. If the pulse is floating and rapid but not hollow, the person is not inherently deficient. Spontaneous resolution involves only sweating, without chills. Generally, if Zheng Qi is strong, pathogens cannot contend, leading to sweating without chills. If Zheng Qi is weak, contention occurs, leading to chills followed by sweating. If there is inner trembling without sweating, Zheng Qi is extremely deficient and unable to expel pathogens, indicating a critical condition.

4. Malaria Paroxysm
Malaria pathogens contend with Wei Qi. Zheng Qi is obstructed by pathogens, internal stagnation prevents reaching the exterior causing exterior cold, and failure to circulate internally causes interior cold, resulting in external shivering and internal trembling.