Another striking fact which has been experimentally established is that the deterioration of these three organs caused by emotion, by exertion, and by other causes is largely counteracted, if not exclusively, during sleep. If animals exhausted by the continued application of a stimulus are allowed complete rest for a certain number of hours, _*without sleep_, the characteristic histologic appearance of exhaustion in the brain, adrenals, and liver is not altered notably, whereas in animals allowed to sleep for the same number of hours the histologic changes in these organs are lessened-- in some cases obliterated even. This significant phenomenon and its relation will be dealt with in a later monograph. Many of the arguments and illustrations by which the primary premises were established are repeated--a few in all--many in more than one of these addresses. It will be observed, however, that the APPLICATION of these premises varies, and that their SIGNIFICANCE broadens progressively. In the Ether Day Address the phylogenetic key supplied by Darwin was utilized to formulate the principle that the organism reacts as a unit to the stimuli of physical injury, of emotion, of infection, etc. To the study of these reactions (transformations of energy) the epoch-making work of Sherrington, "The Integrative Action of the Nervous System," gave an added key by which the dominating role of the brain was determined. Later the original work of Cannon on the adrenal glands gave facts, and an experimental method by which Darwin's phylogenetic theory of the emotions was further elaborated in other papers, especially in the one entitled "Phylogenetic Association in Relation to the Emotions," read before The American Philosophical Society in April, 1911. GEORGE W. CRILE. CLEVELAND, OHIO, _February, 1915_. CONTENTS PAGE PHYLOGENETIC ASSOCIATION IN RELATION TO CERTAIN MEDICAL PROBLEMS. . . . . . . . . . . . . . . . . . . . . . . . . . .1 PHYLOGENETIC ASSOCIATION IN RELATION TO THE EMOTIONS . . . . 55 PAIN, LAUGHTER, AND CRYING. . . . . . . . . . . . . . . . . 77 THE RELATION BETWEEN THE PHYSICAL STATE OF THE BRAIN-CELLS AND BRAIN FUNCTIONS-EXPERIMENTAL AND CLINICAL . . . .111 A MECHANISTIC VIEW OF PSYCHOLOGY . . . . . . . . . . . . . .127 A MECHANISTIC THEORY OF DISEASE. . . . . . . . . . . . . . .157 THE KINETIC SYSTEM . . . . . . . . . . . . . . . . . . . . .173 ALKALESCENCE, ACIDITY, ANESTHESIA--A THEORY OF ANESTHESIA. .227 INDEX. . . . . . . . . . . . . . . . . . . . . . . . . . . .237 THE ORIGIN AND NATURE OF THE EMOTIONS PHYLOGENETIC ASSOCIATION IN RELATION TO CERTAIN MEDICAL PROBLEMS[*] [*] Address delivered at the Massachusetts General Hospital on the sixty-fourth anniversary of Ether Day, Oct. 15, 1910.