As the physiological substratum of emotion, or its material (the reader may use which expression he prefers), comprises the organic or internal functions, and the motor functions showing themselves outwardly, we shall follow this division. Although it may seem artificial, it is not altogether so; the internal manifestations are, for the most part, outside the action of the will; the external manifestations are, in many cases, subject to that action. In any case, this somewhat arbitrary distinction is desirable for the sake of clearness in exposition. I. The relation of different emotions to the internal functions is a subject yet in its infancy. Our knowledge of it is still in a vague and confused state. It is at the same point where the problem of the expression of the emotions was before Charles Bell and Darwin; _i.e._, we have before us a purely empiric set of observed facts without suggested explanation. No doubt it is well known that vaso-motor and respiratory disturbances vary according to the emotions, but the reasons for the differences between one case and another are often unknown and even unexplored. Although Lange has done much in this direction, we cannot congratulate ourselves on having a complete presentation of all the organic and functional manifestations which accompany the simple emotions, not to speak of the complex forms. Still less do we know, clearly and positively, why these and not other manifestations are produced. Thus Hack Tuke asserts it to be a matter of common observation that while the blush of shame begins in the cheeks and the ears, that of anger begins with the eyes, and that of love with the forehead. Supposing this fact to be firmly established, we should still have to find out why, in each case, that particular vascular region should be affected by preference. In short, the study of the external conditions of emotion remains at the present time fragmentary and descriptive. The part played by the viscera in the emotions and passions is so evident that in all ages it has arrested the attention of mankind. On this point, for a period of several centuries, we find, on the one hand, a popular psychology,—which in all languages has become fixed in the form of metaphors,—full of errors and prejudices, but also of very sound observations; on the other hand, scientific attempts at explanation, varying with the physiology of the period, and expressed in terms of the current medical doctrine. During this long period we can distinguish two principal directions of thought: one tending to localise the passions exclusively in the viscera, especially the heart, the other to place them in the brain. Without distorting facts, we might find in these two tendencies the incomplete and unconscious form of the two reigning theories in affective psychology, the organic and the intellectualist.