Biochemist Christian de Duve speaks at a news conference at Rockefeller University after being awarded a share of the 1974 Nobel Prize for medicine or physiology. (Associated Press)

Christian de Duve, 95, a Nobel Prize-winning scientist who was regarded as one of the founders of modern cell biology and helped to show how the work of living cells is carried out by smaller, specialized structures within them, died May 4 in Nethen, Belgium.

The Catholic University of Louvain, where he was professor emeritus, said on its Web site that he had “decided to leave this world” and praised his contributions to medical research. Dr. de Duve shared the 1974 Nobel Prize in Physiology or Medicine with Albert Claude and George E. Palade.

The Belgian newspaper Le Soir said Dr. de Duve, a Belgian citizen, had chosen to die by euthanasia. The practice is legal in Belgium. The newspaper said he gathered his four children around him to end his life, in the words of a daughter, “in great serenity.”

Agence France-Presse quoted Dr. de Duve as saying he had been incapacitated at his home by illness.

His work on cell biology and the mechanisms by which cells work was credited with offering new insights into a variety of maladies and pointing the way toward better treatments.

The honors he received and the esteem in which he was held stemmed from his work on lysosomes and peroxisomes. These are specialized structures found inside cells and are known as organelles, for “little organs.”

The lysosome, Dr. de Duve found, performed digestive activity inside cells. It has been described as carrying out on the cellular level a function similar to that of the immensely larger digestive organs of living beings.

Accounts of Dr. de Duve’s work describe a willingness to go where curiosity and observation led. Imagination, deduction and inference were crucial to his scientific discoveries.

Many techniques he used resembled refinements of common household activities, including grinding up cells and their components in a kitchen blender. He separated heavier portions of ground-up cell material from lighter ones by using a centrifuge.The process works in the same way that cream is mechanically separated from milk.

A key discovery turned on Dr. de Duve’s effort to find what part of a cell made the enzyme phosphatase. His success stemmed from spotting something odd and tracking down the cause.

When cellular material was treated gently before being introduced to the centrifuge, it produced only a small amount of the enzyme. The amount was far less than when the material was subjected to the blender. But gradually, after the mechanical work was over, enzyme levels increased in the gently treated material.

Dr. de Duve realized that the passage of time was slowly breaking down the tough outer membrane of the organelle. The ultimate effect was the same as when the membranes had been quickly chopped up in the blender.

From this observation, he deduced that the enzymes had been produced inside the organelles and had been confined there by the organelle membrane. When the membranes broke, the enzymes leaked out.

Christian Rene de Duve was born Oct. 2, 1917, near London. His parents had fled to England during World War I. They soon returned to Belgium, and he grew up in Antwerp and studied at the Catholic University of Louvain, from which he received a medical degree in 1941 and a PhD in 1945.

Dr. de Duve received additional training in biochemistry at institutions in Sweden and the United States.

He became a full professor of physiological chemistry at Louvain in 1951, studying the action of insulin on the cellular level. The observation of the surprising growth with time of phosphatase led him to drop insulin work and embark on the path that led to the discovery of the lysosome in 1955.

In 1962, he was named a professor at Rockefeller University in New York, while retaining his connection to Louvain. He later founded the International Institute of Cellular and Molecular Pathology in Brussels.

His wife of 65 years, the former Janine Herman, died in 2008. Survivors include four children; two brothers; and seven grandchildren.