The Canton System, enforced by the Qing dynasty, confined foreign traders and missionaries to the southwestern corner of Guangzhou, near the Pearl River. Foreigners could not enter the walled city. They could not travel inland. They operated in a carefully controlled enclave surrounded by walls, regulations, and the ever-present authority of the imperial customs superintendent, known as the Hoppo. Within those constraints, Parker identified the fastest path to Chinese trust: eye disease. Ocular illness was widespread in Canton at the time, and Western medicine had measurably better outcomes for conditions like cataracts and infections than available local treatments. Of the 1,061 patients treated in the hospital's first three months, 96.1 percent had eye conditions. Parker had been told that healing eyes would open doors. He found that it did. Within a year, 2,910 patients had come through.

Success in ophthalmology brought pressure to expand. Patients began arriving with tumors — Parker performed surgery on them, with what the records describe as nearly uniformly successful outcomes — and then with illnesses of every kind. By the end of its first decade, the Canton Hospital was a general medical institution treating the full range of what a nineteenth-century urban population suffered. Parker could not keep up alone. He trained three young Chinese men as medical assistants alongside his colleague Dr. E.C. Bridgman, which was Western-style medical education in China before a formal curriculum existed. The first proper Western medical school in China, the Boji Medical School, opened within the hospital in 1866. It survived the revolutions and reorganizations of the twentieth century and is now part of Sun Yat-sen University of Medical Sciences. Parker also depended financially on local merchants, particularly the prominent Hong merchant Howqua, because he charged patients nothing. The hospital's Chinese name, Pok Tsai, means Universal Helpfulness — a name that described both its reach and its financial model.

In 1840, the First Opium War broke out between Britain and China. The port of Canton was blockaded. Every foreigner was ordered to leave. The hospital closed. Parker evacuated, and the institution that had treated thousands of patients simply stopped — caught in the geopolitics of a conflict driven by trade in a substance that was destroying the communities his patients came from. The irony was not small: Parker had built trust through healing while the larger Western commercial presence in Canton was built on selling opium. When the 1842 Treaty of Nanking ended the war and forced China to open its ports and borders to foreigners, Parker returned to Canton with his wife Harriet Webster, who became the first Western woman granted residence in China. The hospital reopened. It remained under the Medical Missionary Society until 1930, when it became part of Lingnan University.

Among the hospital's patients and eventual students was a young man from Guangdong named Sun Yat-sen. He studied there in the 1880s, taking the medical training that the hospital and its affiliated school provided. The source article identifies Sun Yat-sen as the hospital's most distinguished student — a man who went on to lead the revolution that ended imperial China and became the first provisional president of the Republic of China. The medical education he received in Canton shaped his understanding of reform, pragmatism, and the relationship between knowledge and power. Beyond Sun Yat-sen, the hospital's legacy includes the 1838 founding of the Medical Missionary Society in China, the production of China's first medical journal, and the first X-ray film taken in China. In 1898, Parker's successor John Glasgow Kerr founded the Asylum for the Insane in Canton — the first institution in China dedicated to mental health care. Today the institution continues as the Second Affiliated Hospital of Sun Yat-sen University, a tertiary referral center and still one of China's most prominent ophthalmic institutes.