Marcello Malpighi - Research

Research

Around the age of 38, and with a remarkable academic career behind him, Malpighi decided to dedicate his free time to anatomical studies. Although he conducted some of his studies using vivisection and others through the dissection of corpses, his most illustrative efforts appear to have been based on the use of the microscope. Because of this work, many microscopic anatomical structures are named after Malpighi, including a skin layer (Malpighi layer) and two different Malpighian corpuscles in the kidneys and the spleen, as well as the Malpighian tubules in the excretory system of insects.

See Timeline of microscope technology for more information.

Although a Dutch spectacle maker created the compound lens and inserted it in a microscope around the turn of the seventeenth century, and Galileo had applied the principle of the compound lens to the making of his microscope patented in 1609, its possibilities as a microscope had remained unexploited for half a century, until Robert Hooke improved the instrument. Following this, Marcello Malpighi, Hooke and two other early investigators associated with the Royal Society, Nehemiah Grew and Antoine van Leeuwenhoek were fortunate to have a virtually untried tool in their hands as they began their investigations.

Working on frogs and extrapolating to humans, Malpighi demonstrated the structure of the lungs, previously thought to be a homogeneous mass of flesh, and he offered an explanation for how air and blood mixed in the lungs. Malpighi also used the microscope for his studies of the skin, kidneys, and liver. For example, after he dissected a black male, Malpighi made some groundbreaking headway into the discovery of the origin of black skin. He found that the black pigment was associated with a layer of mucus just beneath the skin.

He was the first to see capillaries in animals, and he discovered the link between arteries and veins that had eluded William Harvey. He may have been the first person to see red blood cells under a microscope. His treatise 'De polypo cordis' (1666) was important for understanding blood composition, as well as how blood clots. In it, Malpighi described how the form of a blood clot differed in the right vs. the left sides of the heart.

The use of the microscope enabled Malpighi to discover that insects (particularly, the silk worm) do not use lungs to breathe, but small holes in their skin called tracheae. Malpighi also studied the anatomy of the brain and concluded that this organ is a gland. In terms of modern endocrinology this deduction is correct because the hypothalamus of the brain has long been recognized for its hormone-secreting capacity.

Because Malpighi had a wide knowledge of both plants and animals, he made contributions to the scientific study of both. The Royal Society in London published two volumes of his botanical and zoological works in 1675 and 1679. Another edition followed in 1687, and a supplementary volume in 1697. In his autobiography, Malpighi speaks of his Anatome Plantarum, decorated with the engravings of Robert White (1645–1703) as "the most elegant format in the whole literate world."

His study of plants led him to conclude that plants had tubules similar to those he saw in insects like the silk worm (using his microscope, he probably saw the stomata, through which plants exchange carbon dioxide with oxygen). Malpighi observed that when a ring-like portion of bark was removed on a trunk a swelling occurred in the tissues above the ring, and he correctly interpreted this as growth stimulated by food coming down from the leaves, and being blocked above the ring.

A talented sketch artist, Malpighi seems to have been the first author to have made detailed drawings of individual organs of flowers. In his Anatome plantarum, there is a longitudinal section of a flower of Nigella (his Melanthi, literally honey-flower) with details of the nectariferous organs. He adds that it is strange that nature has produced on the leaves of the flower shell-like organs in which honey is produced.

Malpighi had success in tracing the ontogeny of plant organs, and the serial development of the shoot owing to his instinct shaped in the sphere of animal embryology. He specialized in seedling development, and in 1679 he published a volume containing a series of exquisitely drawn and engraved images of the stages of development of Legumeninosae (beans) and Cucurbitae (squash, melons). Later he published material depicting the development of the date palm. The great Swedish botanist Linnaeus named the genus Malpighia in honor of Malpighi’s work with plants; Malpighia is the type genus for the Malpighiaceae, a family of tropical and subtropical flowering plants.

Because Malpighi was concerned with teratology (the scientific study of the visible conditions caused by the interruption or alteration of normal development) he expressed grave misgivings about the view of his contemporaries that the galls of trees and herbs gave birth to insects. He conjectured that the creatures in question arose from eggs previously laid in the plant tissue.

Malpighi’s investigations of the life cycle of plants and animals led him into the topic of reproduction. He created detailed drawings of his studies of chick embryo development, seed development in plants (such as the lemon tree) and the transformation of caterpillars into insects. His discoveries helped to illuminate philosophical arguments surrounding the topics of emboîtment, pre-existence, preformation, epigenesis, and metamorphosis.