We thus arrive at a science which may be called paleo-psychology. Its fossils are the thought-forms throughout the ages, and such a science seeks to show fundamental likenesses behind the more superficial dissimilarities. The present work is a contribution to such a science in that it shows the essential relationships of what is found in the unconscious of present day mankind to many forms of thinking of the middle ages. These same trends are present to-day in all of us though hidden behind a different set of structural terms, utilizing different mechanisms for energy expression. The unceasing complexity of life’s accumulations has created a great principle for energy expression—it is termed sublimation—and in popular parlance represents the spiritual striving of mankind towards the perfecting of a relation with the world of reality—the environment—which shall mean human happiness in its truest sense. One of the products of this sublimation tendency is called Mysticism. This work would seek to aid us to an understanding of this manifestation of human conduct as expressed in concrete or contemplated action through thought. It does so by the comparative method, and it is for this reason I have been led to present it to an English reading public. Much of the strange and outre, as well as the commonplace, in human activity conceals energy transformations of inestimable value in the work of sublimation. The race would go mad without it. It sometimes does even with it, a sign that sublimation is still imperfect and that the race is far from being spiritually well. A comprehension of the principles here involved would further the spread of sympathy for all forms of thinking and tend to further spiritual health in such mutual comprehension of the needs of others and of the forms taken by sublimation processes. For the actual work of translation, I wish to express my obligations to friends Wilfred Lay, and Leo Stein. Without their generous and gifted assistance I would not have been able to accomplish the task. SMITH ELY JELLIFFE, M.D. NEW YORK, Oct. 27, 1917. Part I. THE PARABLE. Section I. The Parable. In an old book I discovered an extraordinary narrative entitled Parabola. I take it as the starting point of my observations because it affords a welcome guide. In the endeavor to understand the parable and get a psychological insight into it, we are led on to journey through these very realms of fancy, into which I should like to conduct the reader. At the end of our journey we shall have acquired, with the understanding of the first example, the knowledge of certain psychical laws.