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Medical practice is indeed arduous! Among its difficulties, none is greater than understanding the seasonal patterns, differentiating syndromes (Syndrome Differentiation), and establishing treatment principles. Seasons vary in being warm, hot, cool, or cold; syndromes are distinguished by exterior or interior location, recent onset or latent accumulation; constitutions differ in yin or yang dominance, robustness or weakness; and treatments vary in dispersing, tonifying, purging, or harmonizing. If these distinctions are not made with precision, and prescriptions are administered recklessly, few will avoid causing harm. Yet from ancient times to the present, medical books have piled up like mountains, yet those specifically discussing seasonal diseases (Seasonal Diseases) are scarce. Out of reverence for my late father's aspirations, and disregarding the hardship of explaining things plainly, I have specially elaborated on this theory.

My late father, whose pseudonym was Yixian, loved reading and reciting poetry. He once drank wine and composed poems with Xu Xiaolian Yefan from Wulin, Yu Xiaolian Yuanpu from Longqiu, and Xu Maocai Yue, engaging in mutual poetic exchanges. He authored *Yanghe Shanfang Shigao* (Poetry Manuscript of the Crane-Nurturing Mountain Studio). Later, he abandoned Confucian studies to learn traditional Chinese medicine (Qi-Huang Arts) under Master Cheng Zhitian, and subsequently practiced medicine in Longqiu. In his later years, he compiled various ancient medical texts into forty volumes titled *Yibo* (Comprehensive Medical Knowledge), and also wrote four volumes of *Yiyue* (Medical Principles). The book contained many insights that had not been previously expressed by others; numerous friends borrowed it for copying, all praising it highly. In the spring of the tenth year of the Xianfeng era, my neighbor Yu Gongchen Mingjing provided funds to encourage him to print the works. Just as printing was being discussed, a sudden upheaval forced us to flee hastily, and the books were lost. At that time, my father and I returned to Ke City. To preserve the documents, we sought the original manuscripts from those who had borrowed them, ensuring that my father's decades of accumulated effort would not be lost to oblivion. However, within less than two years, my father passed away suddenly. Alas! The *Book of Rites* states: "After the father's death, if the son cannot read the father's books, it is because the traces of the father's hand remain." I sought my father's handwritten traces but could no longer find them. Reflecting alone at night, I could not help but shed tears. Now, only hundreds of case records remain, which I recorded while attending him. These include discussions on seasonal diseases. I entrusted them entirely to my students Cheng Xi and Jiang Cheng to annotate in detail and compile into four volumes. While reading them, it feels as though I can still hear the questions and answers from my father's teachings in the courtyard.

I recall my father once telling me: "In a year, miscellaneous diseases are few, while seasonal diseases are many. If one does not study the methods for treating seasonal diseases in daily life, one will inevitably be at a loss when facing clinical cases." I kept this in mind respectfully and have never forgotten it. Alas! It has been over twenty years since my father's passing. I have extensively studied the works of various masters, drawing inferences and making connections, gradually gaining personal insights. I often wished to publish my humble opinions for the world, hoping that those who understand me might correct my deficiencies. Yet, ashamed of being a commoner with talent as short and fragmented as sock threads, fearing ridicule from the refined scholars, I repeatedly halted. However, my like-minded colleagues insisted on hearing my views on seasonal diseases, pressing their requests incessantly. Therefore, without presuming upon my shallow learning, I have taken the eight sentences from the *Da Liao Yin Yang Ying Xiang Lun* (Great Treatise on the Correspondence of Yin and Yang): "Those injured by cold in winter will suffer from warmth diseases in spring; those injured by wind in spring will suffer from undigested food diarrhea in summer; those injured by heat in summer will suffer from malaria in autumn; those injured by dampness in autumn will suffer from cough in winter," as the overarching framework of this book. Combining this with the teachings of sages past and present, I have written this volume to fulfill my duty. First, I discuss the diseases, addressing their normal patterns; second, I discuss treatment cases, addressing their variable manifestations. I believe that if one knows the normal patterns and understands the variations, seasonal diseases will not be difficult to treat. I hope that those who understand the seasons, according to the climatic characteristics of spring warmth, summer heat, autumn coolness, and winter cold, can distinguish between newly acquired pathogens and latent qi, further examine the constitution's deficiency or excess, and apply dispersing or tonifying methods accordingly. Thus, although medical practice is difficult, by tackling its greatest challenges, it ceases to seem difficult. I wish that readers of this book would not fear difficulty. This is the preface.

On the day before the Mid-Autumn Festival of the Renwu Year, the eighth year of the Guangxu Era, Lei Feng, courtesy name Shaoyi, from Sanqu, inscribed at the Crane-Nurturing Mountain Studio.