In the Lehrbuch, Leydig reviewed the crucial developments in the history of histology, including the discovery and definition of the cell by Jan Evangelista Purkyne (1797–1869), Gabriel Gustav Valentin (1810–1883), and by Theodor Ambrose Hubert Schwann (1810–1882), who described the cell as a vesicle containing a nucleus in 1839. Leydig paid further tribute to other contemporary anatomists, particularly Johannes Peter Müller (1801–1858) for his work on glands and emphasizing cellular doctrine for pathology.
Leydig's Lehrbuch reviewed key developments in histology, highlighting the discovery of the cell by Purkyne, Valentin, and Schwann, who defined it as a vesicle with a nucleus in 1839. He also acknowledged the contributions of Müller to understanding glands and their role in cellular pathology.