Also in 1835, he was the first to describe protoplasm, the jellylike material in animal cells which he called sarcode (from the Greek word σάρξ, meaning “flesh”). [Hugo von Mohl is credited with introducing the name protoplasm for it in 1846.] This substance, now called cytoplasm, was later found in living plant cells. Although the term protoplasm is rarely used any more in a strictly scientific sense, many of the notions associated with the term have survived. Thus it is still accepted that all living organisms are made largely of the same classes of substances such as salts and organic molecules, that some of these are organized into structures large enough to be seen in the microscope, and that water almost always is by far the most abundant material.
Dujardin’s written works include Histoire naturelle des infusoires (1840), Manuel de l’observateur au microscope (1842), and Histoire naturelle des helminthes (1844).