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Cancer causes: Theories throughout history

From the earliest times, physicians have puzzled over the causes of cancer. The Egyptians blamed cancers on the gods.

Humoral theory: Hippocrates believed that the body had 4 humors (body fluids) -- blood, phlegm, yellow bile, and black bile. When the humors were balanced, a person was healthy. Too much or too little of any of them caused disease. An excess of black bile in various body sites was thought to cause cancer. This theory of cancer was passed on by the Romans and was embraced by the influential doctor Galen’s medical teaching, which remained the unchallenged standard through the Middle Ages for over 1300 years. During this period, the study of the body, including autopsies, was prohibited for religious reasons, thus limiting knowledge.

Lymph theory: Among theories that replaced the humoral theory of cancer was cancer's formation by another fluid, lymph. Life was believed to consist of continuous and appropriate movement of the fluid parts through solids. Of all the fluids, the most important were blood and lymph. Stahl and Hoffman theorized that cancer was composed of fermenting and degenerating lymph varying in density, acidity, and alkalinity. The lymph theory gained rapid support. The eminent surgeon John Hunter (1723–1792) agreed that tumors grow from lymph constantly thrown out by the blood.

Blastema theory: In 1838, German pathologist Johannes Muller demonstrated that cancer is made up of cells and not lymph, but he believed that cancer cells did not arise from normal cells. Muller proposed that cancer cells arose from budding elements (blastema) between normal tissues. His student, Rudolph Virchow (1821–1902), the famous German pathologist, determined that all cells, including cancer cells, are derived from other cells.

Chronic irritation theory: Virchow proposed that chronic irritation was the cause of cancer, but he falsely believed that cancers "spread like a liquid." A German surgeon, Karl Thiersch, showed that cancers metastasize through the spread of malignant cells and not through some unidentified fluid.

Trauma theory: Despite advances in the understanding of cancer, from the late 1800s until the 1920s, trauma was thought by some to cause cancer. This belief was maintained despite the failure of injury to cause cancer in experimental animals.

Parasite theory: In the 17th and 18th centuries, some believed that cancer was contagious. In fact, the first cancer hospital in France was forced to move from the city in 1779 because of the fear of the spread of cancer throughout the city. Although human cancer, itself, is not contagious, we now know that certain viruses, bacteria, and parasites can increase a person's risk of developing cancer.
So what is your theory with regard to the present reasons for cancer? Mine is the food we get to eat is not as nutritious as it was even two decades ago. The quality of our water and air has deteriorated. We are subjected to a larger number of carcinogens than we have before. Our diet and lifestyle are also great factors. We have become a society that lives to eat, and not eat to live. We are barraged by advertisements to consume foods that are not fit for human consumption and are full of additives. We do not exercise enough.
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