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William Harvey argued in 1628 that blood circulates, but he had a gap in his argument. Blood leaves the heart in arteries and comes back in veins, so the two must be connected somewhere. Harvey could not see the connection. Marcello Malpighi did, a generation later, using a microscope and a frog. This post covers his life, the capillary discovery, his other work, and the two NCERT terms that carry his name and confuse students.
Who was Marcello Malpighi?
A 2021 historical note in Arquivos de Neuro-Psiquiatria gives the outline. Malpighi lived from 1628 to 1694 and is often called the founder of microscopic anatomy. He took degrees in philosophy and medicine in 1653 and held professorships at the universities of Bologna, Pisa and Messina. He was introduced to the microscope at Pisa in 1656 and was apparently one of the first to use the compound instrument, with an objective lens and an eyepiece. In 1691 he moved to Rome as personal physician to Pope Innocent XII.
The note lists organs he studied under the microscope: liver, brain, lung, heart, kidney, spleen, skin and tongue. He also studied the development of the chick embryo, insects and plants.
How did Malpighi find the capillaries?
The introduction to the Project Gutenberg edition of Harvey's De Motu Cordis puts it plainly. Harvey bridged the gap between arteries and veins by reasoning, because his eyes "with the imperfect instrument then alone at his disposal" could not. Then, "four years after Harvey's death", Malpighi in 1661 observed "the capillaries uniting by their networks arteries and veins".
He did it with frogs. A 2013 review by John West in the American Journal of Physiology explains that his lung work was chiefly carried out on the frog, an animal he called the "microscope of nature" because its thin, simple tissues showed structures not visible in larger animals. West describes him as known above all as the discoverer of the pulmonary capillaries and of the alveoli, the tiny air sacs of the lung.
William Locy's 1908 history Biology and Its Makers adds the detail. Before Malpighi, lungs were thought of as a fairly uniform fleshy mass. He showed air cells, and the idea that air and blood come close but are always separated by a membrane. He watched blood moving through capillaries in the transparent lung of the frog and in its mesentery.
Why use a frog to study human lungs?
West notes that Malpighi argued nature tries out its great works in simpler animals before building them in larger ones. Put in modern terms, he was using a model organism. A frog's lung is thin enough to see through, so a structure too small and too deeply buried to see in a mammal becomes visible. He then applied what he saw to human lungs by analogy. Biology still works this way, with fruit flies, mice and bacteria standing in for harder systems.
What other structures carry Malpighi's name?
Locy lists several. His 1669 monograph on the silkworm, published by the Royal Society of London, described the insect's gut and the fine tubules attached to it, now called Malpighian tubules. He described a layer of the skin, still called the Malpighian layer, and his name is attached to corpuscles in the kidney and the spleen. West adds that he discovered the spiracles and tracheae through which insects breathe.
Common mistakes: Malpighian tubules or Malpighian body?
NCERT uses his name in two very different places, and mixing them up costs marks.
Malpighian tubules are excretory organs in insects. The NCERT Class 11 chapter on excretory products says they are the excretory structures of most insects, including cockroaches, and help remove nitrogenous wastes.
Malpighian body (also called the Malpighian or renal corpuscle) is part of the human nephron. The same chapter describes it as the glomerulus together with Bowman's capsule.
A quick check: tubules belong to insects, the body or corpuscle belongs to the kidney. Our guide to excretory products for NEET covers the nephron in detail.
A second mistake is to say Malpighi discovered circulation. Harvey proposed and argued for circulation. Malpighi supplied the visual proof of the link.
What can a student learn from how Malpighi worked?
Look for the missing piece in an argument. Harvey's theory predicted a connection. Malpighi went looking for it. When you learn a process, ask which step you are taking on trust.
Choose the right specimen. The frog made the invisible visible. In practicals, a thin section or a simple organism often shows more than a complex one.
Compare across organisms. Malpighi studied insects, frogs, chicks and plants, and used each to understand the others.
Our post on William Harvey and the circulation of the blood explains the argument that Malpighi completed. If capillary exchange or the nephron is still hard to picture, the Fermi Simulation Lab has interactive simulations for ideas that are easier to see than to read.
Practice routine: write two lines each on Malpighian tubules and the Malpighian body, covering the organism, the system and the function, then check both against NCERT.
Next step: draw a nephron from memory, label the Malpighian body, and mark where the capillaries of the glomerulus sit.
