I shall not repeat in these pages for the hundredth time the criticism of temperaments as they were described by the ancient schools, and which I have expounded in many of my works, small and large. Not everybody has accepted my standards of classification, but all agree with me in the belief that temperaments have had their time, and that hygiene, medicine, psychology await from the progress of modern physiology the elements to determine, as science requires, the physical and moral characteristics of a human individual. Against this impotency of modern physiology I have protested, changing the name of "temperament" to that of "individual constitution": innocent revenge of all men who, when powerless to change a thing, satisfy their rage by changing its name. Every man loves in his own way and, as we bring to love the greatest possible tribute of psychical elements, it follows that human loves differ more than hatreds, more than the manners of eating, of motion, of will. The lower we descend from the branches to the trunk, the more human elements resemble each other; the higher we ascend to the loftiest branches of the tree, the more the elements diverge and differ. Ask a woman of easy virtue, or a Don Juan, how many are the methods of loving, and they both not only will answer that every one loves in a different manner, but will add that the manners themselves are so extraordinarily different that calling all these most variform ways of loving by the one name of the same sentiment excites repugnance. It is true that some authors have amused themselves by describing a "sanguine love," a "nervous love," a "lymphatic love," a "hepatic love"; but these pictures are innocent pastimes, arabesques traced on the epidermis of human nature, and the schools of psychology and literature, which succeed each other, so completely obliterate these arabesques that not the least trace of them is left. Even when, instead of the caricatures of temperaments, we should succeed in delineating a true family of human constitutions, it would be very difficult to class under it all forms of love. The thousands and thousands of color cases of the Roman mosaic-maker are sufficient to classify the innumerable tints that an expert eye succeeds in discerning; but who will give me a palette so gigantic that I may spread on it all the polychromic mixtures, all the simple and compound colors, all the proteiform iridescences offered by the human light when it strikes the powerful prism of love? The question as to the quantity of love which an individual may feel is the easiest to solve; but it is also one of the most important. In every psychological problem there is an element of quantity; and as it is the simplest, it is also the most visible. It is, I would almost say, the skeleton of the phenomenon and we should grasp it eagerly, as the thread which guides us through the labyrinth of these studies.