This translation has been made from the second revised and supplemented Rus­ sian edition, published by the State Med­ ical Publishing House, Moscow 1952.On the occasion of the centenary of Pavlov’s birthday (September 27, 1949) the author of this book lakes the liberty of attempting to fill this gap in the patho-physiologv of the higher nervous activity; his aim is to expoundin a number of essays the basic achievements of thi's young branch of science and to give an outline of its development in the Pavlov school (including its ramifica­tions) up to our lime.In the preface to the third edition of the lectures on the Work of the Cerebral Hemispheres published in No­vember 1935, Pavlov wrote: “My new systematic exposi­tion of the whole of our experimental material in the shape of one book will require much labour, and I regard it as my last scientific task. It will take years to complete this work. If only fate will be so kind as to preserve for me at my age the vigour that will enable me to carry out this important duty of my life!’Death prevented Pavlov from carrying out this desire.In the Essays on the Patho-Physiology of the Higher Nervous Activity the author tries, to the best of his ability, to carry out, even in small measure, Pavlov’s will; the author regards this as his duty to Russian science and to his late teacher.