Max Schultze. Portrait of Max Johann Sigismund Schultze (1825-74), German biologist. Schultze studied the anatomy of a number of animals, particularly single-celled ones. As a result of these studies he defined the concept of a cell in 1861. He defined a cell as a nucleus surrounded by a protoplasm and stated that it was the basic building block of all organisms. Whilst studying the eye retinas of birds, Schultze discovered that there were two types of light-receiving nerve endings and proposed that these rods and cones functioned separately. It is now known that the rods detect dim light whilst the cones are used to spot details in bright light.