Heredity is a prominent factor in the etiology of many nervous diseases, including Friedreich's ataxia, hereditary spastic paraplegia, Huntington's chorea, amaurotic family idiocy and other similar conditions. They are all degenerative, and therefore may be termed heredodegenerative. Though differing clinically and pathologically, the majority of heredodegenerations, if not all, possess, according to Schaffer, certain fundamental histopathologic or morphologic features that are specific and common to all. The specific nature of such changes has been the subject of many publications by this indefatigable and brilliant neuropathologist, and the results of his twenty years' studies are incorporated in the present volume, dedicated to the Spanish neurohistologist Ramón y Cajal. Schaffer maintains that all heredodegenerative diseases are endogenous, the result of the disease of the hyaloplasm—the undifferentiated portion of the cytoplasm; only the neural ectodermal derivatives—the ganglion and glia cells—are affected, either as a whole, resulting in a condition known as amaurotic family