The Death of the Humoral Theory of Disease

When last we left the humoral theory of disease, it had survived the debunking efforts of Vesalius and Baillie. 黑胆汁可能不存在, but investigators found other body fluids besides blood, 痰, and yellow bile to take its place. 在17世纪, an Italian physician named Gaspare Aselli discovered the small lymphatic channels, the conduits through which the extracellular fluid called lymph flows and eventually returns via the thoracic duct to the circulation of the blood. Aselli proposed that abnormalities of lymph might account for cancer; after all, tumors often appeared within the bead-like structures arrayed along the lymphatics that we know as lymph nodes. Such was the staying power of this paradigm of human disease that the humoral theory hung around until the middle of the nineteenth century when the development of cell theory finally put it down for good.

The independent but complementary observations of Theodor Schwann and Mattias Schleiden in animal and plant tissues led the two friends in 1838 to propose the fundamental axioms of cell theory: all living organisms are composed of cells, and cells are the basic units of life. 几十年后, the renowned Prussian pathologist Rudolf Virchow added the third axiom that all cells come from pre-existing cells. Virchow was also the first to suggest that cancer cells arise from previously normal cells, although his ideas about how this might occur proved erroneous. 到19世纪末, the combined observations of Robert Koch, 路易·巴斯德, and Robert Lister established the germ theory of disease, and the obituary of the humoral theory of disease was written.

但是癌症呢?? Could the germ theory account for this disease? An infectious cause for cancer was not immediately apparent, although researcher Peyton Rous discovered the first recognized carcinogenic (cancer-inducing) virus in the 1910s. 这种病毒传播了肉瘤, a type of cancer affecting muscles, 骨, 类似的组织, 在鸡身上. Subsequent work has implicated several other viruses in human cancers: Epstein-Barr virus in a particularly aggressive type of lymphoma named for its describer, Dennis Burkett; human papilloma virus, linked to many cancers of the cervix, 肛门, and head and neck region; hepatitis B and C virus and primary liver cancers; and one of the herpesviruses and an unusual skin cancer called Kaposi sarcoma. But I am now well ahead of myself in my pursuit of explanations for cancer.

Medical observers had determined that cancers often developed in persons exposed to various environmental or industrial substances. Percivall Pott gets the credit for being the first to make the link after observing the plight of young chimney sweeps, chronically covered in soot that often accumulated in the folds of undergarments, susceptible to skin cancers involving the genitals. Several of the early researchers who worked with radioactive substances, 比如皮埃尔和居里夫人, succumbed to cancers if they did not first die of radiation poisoning. And burgeoning industrialization in the west brought new health perils to workers, including cancers induced by long-term exposure to various chemicals.

That cancer has several different causes became increasingly clear. What remained elusive was an explanation. How do we get from cause to effect? 癌症的本质是什么? If not the effect of “evil” humors, if not excessive lymph accumulation, if not (mostly) germs, what? 接下来我们要谈这个问题.