Malpighi observes capillaries

Harvey’s circulation left a connection to be observed directly: how blood leaving arteries reaches veins. The vessels involved were too small for ordinary inspection. Marcello Malpighi used microscopes on animal tissues and selected thin, translucent specimens. In 1661 he described observations of frog lungs in letters to Borelli. Their small vessels provided a visible connection within the route proposed by the theory of circulation.

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Light passing through frog lung tissue made a network of tiny channels distinguishable. Preparation, illumination, and lenses determined whether details were clear, so microscopic anatomy demanded new techniques. Malpighi also examined lungs, liver, kidneys, insects, and plants. Organs could be investigated beyond their outlines and visible parts. Fine internal structures became objects of description, and their relations to bodily functions required further experiments and comparison.

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Capillary observation supplemented the argument for circulation. Later physiology investigated exchanges between blood and tissues. Microscopes gave medical teaching another level of anatomical detail. Comparisons between animals and plants helped identify shared forms and differences. Malpighi’s publications and letters preserved the observations. Histology subsequently developed through improved sections, stains, and lenses, making parts of the body that were inaccessible to ordinary sight available for systematic investigation.

References: [1]