This book presents the results of Prof. A. D. Speransky's scientific investigations, including 46 illustrations, on the effects of disease in causing changes in the nervous system. Contrary to the general view that disease arises from the victory of an invading microbe over the defensive resources of the organism, the author argues that not only the course but the cause of the disease changes with every stage. It is a process depending on the interaction of many parts. Speransky's work in neurophysiology was groundbreaking and is still an important contribution today if one actually reads and studies his results. His research illustrates the fundamental problem of finding a means to create groupings of nerve combinations in the nervous system without causing a new source of irritation, such as is produced by surgical operation or the introduction of vaccines in the blood. He discusses in detail the valuable results attained in his experiments.