Chapter 8: The Principle of Yin and Yang

After parting ways with Huang Yaoshi, the two quickly returned to Li Yu's consultation room. It just so happened that the previous patient was stepping out.

"Teacher Li, this medicine is truly miraculous!" Zhang Jing could not help but exclaim with excitement as soon as they entered.

Li Yu remained calm, asking indifferently, "Has the fever subsided?"

Before Zhang Jing could speak, the female patient chimed in eagerly, "Yes, yes, Director Li! Not only is the fever gone, but the aches all over my body have vanished too. I feel as if my illness has been cured instantly. You are truly a miraculous doctor!"

"Madam, please do not shower me with such grand titles. I am not a miraculous doctor, nor am I a director; just calling me Doctor Li will suffice," Li Yu replied with a modest wave of his hand.

Compared to the unwavering confidence he displayed during the examination, he seemed like an entirely different person. Seeing this, Zhang Jing’s admiration deepened even further. He sighed to himself: confident but not arrogant, humble but not self-deprecating. This is exactly what a great physician should be.

"Teacher Li, the patient was mainly asking if you needed to prescribe any follow-up herbal formulas to take home?"

"No need. Judging by the pulse, the patient’s constitution is generally good; this illness was likely just the result of a severe flu." He then turned to the patient and added, "How about this: go home, change out of your sweat-drenched clothes, eat light for a few days, and rest. Your body will return to its original state soon."

"Alright, alright, thank you Director—I mean, thank you, Doctor Li. Thank you!"

Shortly after the patient left, the next one arrived. Zhang Jing continued to record the medical history and copy down the prescriptions, occasionally answering questions posed by Li Yu. Although he could provide the answers Li Yu expected most of the time, Zhang Jing knew clearly that this was largely due to Li Yu’s guidance from the sidelines. If he were forced to face patients and conduct consultations independently at this moment, he would likely be at a total loss nine times out of ten.

This was to be expected, as clinical syndrome differentiation is no simple task. Most patients who come to the National Medicine Hall suffer from difficult, stubborn ailments that have failed to respond to other treatments. The conventional methods of differentiation found in textbooks simply do not work here.

Zhang Jing had specifically inquired and learned that all consultation rooms at the National Medicine Hall operated on an appointment-only basis. However, the limit on the number of patients per doctor varied; Li Yu limited his daily intake to 32 patients, meaning 16 in the morning, with fifteen minutes allotted per person. Zhang Jing knew that many traditional Chinese medicine clinics also set limits, but most did so merely for "hunger marketing" to create a false sense of popularity.

Li Yu was clearly different; his limits were set to ensure every patient received ample time, reflecting his deep sense of responsibility. For a true practitioner of traditional Chinese medicine, economic gain is never the primary concern—efficacy is.

Through his observations over the morning, Zhang Jing noticed a curious phenomenon. Unlike most high-quality TCM clinics, Li Yu had very few follow-up patients. Upon reflection, this was easy to explain. Highly skilled TCM practitioners usually achieve good results, but their treatment courses are often long, leading to many repeat visits. However, for a master of Li Yu’s caliber, a single consultation and a few doses of medicine, or sometimes even just one, were enough to resolve the issue. Why would there be a need for follow-up?

At lunch in the clinic cafeteria, Zhang Jing recalled the topic they hadn't finished discussing. He continued to seek Li Yu’s counsel: "Teacher Li, you previously said that all things can be divided into Yin and Yang; thus, syndromes have Yin and Yang, pulses have Yin and Yang, and medicines have Yin and Yang. Regarding the pulse, signs like 'floating, large, slippery, and rapid' are all Yang, while 'sinking, faint, fine, and rough' are all Yin. So, when taking a pulse, how should one distinguish Yin and Yang between the left and right?"

"Xiao Zhang, that is a great question. The *Su Wen: Treatise on the Correspondence of Yin and Yang* states: 'The left and right are the pathways of Yin and Yang.' Tell me, how do you interpret this?" Li Yu set down his chopsticks and asked in return.

"The ancients stood facing south, so left and right corresponded to east and west. The east is where the sun rises, and the west is where it sets. Therefore, the left governs ascent, and the right governs descent. In its primitive sense, Yin and Yang refer to the orientation toward or away from sunlight. Here, the sun is Yang, and its rising in the east and setting in the west creates a trajectory, which is called a 'pathway.' Thus, the left and right are the pathways of Yin and Yang."

"Good!" Li Yu nodded slightly and continued, "Now, think about your earlier question again."

As Zhang Jing pondered, Li Simeng interjected, "Do we even need to think about it? It’s obviously left-Yang and right-Yin, because ascending is Yang, and Yang qi represents the upward growth of life."

Unexpectedly, Li Yu gently reprimanded her: "Simeng, don't cause trouble!"

"How is that causing trouble? He couldn't answer it himself, so why can't others? I think Master is just biased. I don't believe he can come up with a different answer this time," Li Simeng said, looking aggrieved.

Zhang Jing ignored her and continued to mull over the seemingly simple question. He remembered clearly that even to this day, there remains a debate in the TCM community over whether the left is Yin and the right is Yang, or vice versa.

After a long while, a flash of insight struck him. "Teacher Li, I think I understand. It is neither left-Yin/right-Yang nor left-Yang/right-Yin. The sun rising from the east and setting in the west merely describes the trajectory of Yang qi. It reflects the natural phenomenon where Yang qi emerges at dawn, gradually rising from the left until it reaches its peak at noon, at which point it is at its strongest. Afterward, it begins to descend toward the right, gradually waning until the sun sets behind the mountains."

Li Simeng was left completely bewildered by this explanation. Li Yu, however, couldn't help but applaud: "Xiao Zhang, your intuition is truly excellent! The Great Dao is simple. The Dao is the source of all things in the universe; it gives birth to the One, and the One gives birth to the Two, which is the way of Yin and Yang. Therefore, everything is inseparable from Yin and Yang. Your understanding has begun to touch upon the essence of the theory of Yin and Yang."

Zhang Jing scratched his head, not because of the praise, but because a giant question mark had appeared in his mind. The theory of Yin and Yang is the soul of TCM. Yet, it has a name but no form—it is neither visible nor tangible—which is often criticized by Western medicine. To the uninitiated, the term "Yin and Yang" sounds mystical and obscure. Of course, this includes a significant number of so-called industry insiders who never truly grasped TCM.

"Let me ask you this: since you know that the Taiyang is Three-Yang, Yangming is Two-Yang, Shaoyang is One-Yang, Taiyin is Three-Yin, Shaoyin is Two-Yin, and Jueyin is One-Yin, how would you use the Three-Yin and Three-Yang system to describe the changes between day and night?" Li Yu smiled, prompting him.

Zhang Jing fell into deep thought again. Li Simeng couldn't hold back and raised her hand: "Master, I know this one."

"Go ahead, Simeng."

"From 3 to 5 AM, the Yin hour, corresponds to the Hand Taiyin Lung Meridian; 5 to 7 AM, the Mao hour, to the Hand Yangming Large Intestine Meridian; 7 to 9 AM, the Chen hour, to the Foot Yangming Stomach Meridian; 9 to 11 AM, the Si hour, to the Foot Taiyin Spleen Meridian. 11 AM to 1 PM, the Wu hour, to the Hand Shaoyin Heart Meridian; 1 to 3 PM, the Wei hour, to the Hand Taiyang Small Intestine Meridian; 3 to 5 PM, the Shen hour, to the Foot Taiyang Bladder Meridian; 5 to 7 PM, the You hour, to the Foot Shaoyin Kidney Meridian. 7 to 9 PM, the Xu hour, to the Hand Jueyin Pericardium Meridian; 9 PM to 11 PM, the Hai hour, to the Hand Shaoyang Triple Burner Meridian; 11 PM to 1 AM, the Zi hour, to the Foot Shaoyang Gallbladder Meridian; 1 to 3 AM, the Chou hour, to the Foot Jueyin Liver Meridian."

Having recited the entire *Zi-Wu Flow* in one breath, Li Simeng was slightly out of breath and said to Zhang Jing with a provocative tone, "Junior brother, feel free to point out any mistakes."

Zhang Jing didn't mind her tone at all, but gently shook his head: "It's wrong. I don't think that's right."

"Wrong?" Li Simeng frowned, full of confusion. "I have the *Zi-Wu Flow* memorized perfectly; how could it be wrong?"

"It’s not that you memorized it wrong, but that the Zi hour corresponds to the Shaoyang Meridian—I believe that is incorrect."

"Then tell me, what should it correspond to?" Li Simeng asked testily.

"The Zi hour is when the One Yang is born. When Yin reaches its extreme, Yang is born. The Zi hour is the time when Yin qi is heaviest, but also when Yang qi begins to grow. While Shaoyang is a 'weak Yang,' it is still Yang. Therefore, the two clearly do not match."

As soon as he finished speaking, Li Yu said "Good" twice in a row.

"Xiao Zhang, you are very good at thinking. Now, I can hand you the key to unlocking the mysteries of the *Shanghan Lun*."

The key to the mysteries? Zhang Jing was instantly filled with anticipation! As the ancestor of medicinal formula books and the pioneer of syndrome differentiation and treatment, the *Shanghan Lun* is revered by physicians throughout the ages. The influence of the Medical Sage Zhang Zhongjing on the field of TCM is profound. From Wang Shuhe of the Jin Dynasty and Sun Simiao of the Tang Dynasty, to the Four Great Masters of the Jin-Yuan period—Liu Wansu, Zhang Congzheng, Li Gao, and Zhu Danxi—as well as Qing Dynasty physicians like Ye Tianshi and Wu Jutong, all were followers of Zhongjing’s teachings before making their own contributions.

For over a thousand years, the TCM world has been striving to uncover the mysteries of the *Shanghan Lun*. In other words, everyone has been searching for the key to decipher it. What, then, would the key mentioned by Li Yu turn out to be?