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I have said that Yu Shuji (a historical figure/author) used birds and beasts to record seasonal changes, and the *Yueling* (Monthly Ordinances) used insects and fish for divination. This is using natural phenomena to verify the Heavenly Dao. The *Neijing* (Inner Canon) diagnoses diseases by examining bodily fluids, while later generations differentiate syndromes by analyzing phlegm and saliva. This is using human physiological substances to verify the Human Way. Generally, the Heavenly Dao is distant, while the Human Way is proximate. One draws analogies from things far away and from one's own body. Although the objects of observation differ, the underlying principles are identical. Moreover, phlegm arises from disease, and the disease becomes manifest through phlegm; this is a matter of principle that is extremely clear and obvious.

Occasionally consulting ancient texts, I hold that phlegm (*Tan*) is thick and turbid, whereas fluid retention (*Yin*) is thin and clear. Cold-phlegm is greenish, damp-phlegm is white, fire-phlegm is black, heat-phlegm is yellow, and old-phlegm (*Lao Tan*) is gelatinous and sticky. Phlegm that is slippery and easy to expectorate belongs to Spleen-dampness (*Shi Tan*). Phlegm that is dry and difficult to expectorate belongs to Lung-dryness (*Zao Tan*). Phlegm that is clear and foamy belongs to Liver-wind (*Feng Tan*). Phlegm that is hard and forms clumps belongs to Heart-heat (*Re Tan*). Phlegm with black spots and a thinner consistency belongs to Kidney-cold (*Han Tan*). In new and mild diseases, the phlegm is white/clear and thin. In long-standing and severe diseases, the phlegm is yellow/turbid and sticky/copious. Excessive salivation indicates Stomach-cold. Drooling indicates Spleen-cold. Difficulty in speaking with froth spitting from the mouth indicates pathogenic factors invading the Zang organs. Abdominal pain occurring intermittently with drool spitting indicates intestinal roundworms (*Hui Chong*) disturbing the interior. Coughing up saliva and froth, with an open mouth and shortness of breath, are signs of Lung萎 (*Fei Fei*, Lung Flaccidity). Coughing up pus and blood, with dry mouth and chest pain, are signs of Lung Abscess (*Fei Yong*). Vomiting material resembling rice porridge with a fishy and foul odor are all indications of Lung Abscess. Phlegm resembling rotten cotton wool or coal dust represents the appearance of Old-phlegm. These texts diagnose the depth of disease based on the form and color of phlegm and saliva.

Some argue that when the sound of phlegm corresponds with symptoms, the condition is mild; when they do not correspond, it is severe. A change from thin to thick indicates the disease is receding daily; a change from thick to thin indicates the disease is advancing daily. Hemoptysis caused by violent coughing often originates from external contraction. Coughing with phlegm caused by hemoptysis often belongs to internal injury. These can also be cross-referenced with other symptoms. Synthesizing these observations and analyzing them discursively: thin substances are Fluid Retention (*Yin*), thick substances are Phlegm (*Tan*). Clear substances indicate deficiency of Qi and Form (Zheng Qi), while turbid substances indicate excess of Pathogenic Qi. Greenish-white phlegm suggests little Heat, while yellow-red phlegm suggests abundant Heat. Thus, variations in the form and differences in the color of phlegm can all be deduced and judged through this method.