The process of digestion, whereby food is broken down into molecules that can be transported around the body by the bloodstream and absorbed by cells, was largely a mystery until the 18th century. The breakthrough in understanding came when Italian biologist Lazzaro Spallanzani found that gastric fluids contain specific chemicals that are crucial to the decomposition of food.
Before Spallanzani, physicians held competing theories about the process. Some considered that heat within the body “cooked” food to produce energy. One school of thought likened digestion to fermentation, while another argued that food pieces were simply ground up in a mechanical process, known as trituration.
Vitalism, an even older theory that dated back to the ancient world, was championed by Aristotle and persisted into the 19th century. It held that bodily processes were driven by a spiritual life force and argued that something as miraculous as digestion could not be explained in just physical terms.
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