Yet it is as unreasonable to take normal phenomena for granted here as in any other region of science. A knowledge of such phenomena is as necessary here as physiology is to pathology or anatomy to surgery. So far from the facts of normal sex development, sex emotions, and sex needs being uniform and constant, as is assumed by those who consider their discussion unnecessary, the range of variation within fairly normal limits is immense, and it is impossible to meet with two individuals whose records are nearly identical. There are two fundamental reasons why the endeavor should be made to obtain a broad basis of clear information on the subject. In the first place, the normal phenomena give the key to the abnormal phenomena, and the majority of sexual perversions, including even those that are most repulsive, are but exaggerations of instincts and emotions that are germinal in normal human beings. In the second place, we cannot even know what is normal until we are acquainted with the sexual life of a large number of healthy individuals. And until we know the limits of normal sexuality we are not in position to lay down any reasonable rules of sexual hygiene. On these grounds I have for some time sought to obtain the sexual histories, and more especially the early histories, of men and women who, on _prima facie_ grounds, may fairly be considered, or are at all events by themselves and others considered, ordinarily healthy and normal. There are many difficulties about such a task, difficulties which are sufficiently obvious. There is, first of all, the natural reticence to reveal facts of so intimately personal a character. There is the prevailing ignorance and unintelligence which leads to the phenomena being obscure to the subject himself. When the first difficulty has been overcome, and the second is non-existent, there is still a lack of sufficiently strong motive to undertake the record, as well as a failure to realize the value of such records. I have, however, received a large number of such histories, for the most part offered spontaneously with permission to make such further inquiries as I thought desirable. Some of these histories are extremely interesting and instructive. In the present Appendix, and in a corresponding Appendix to the two following volumes of these _Studies_, I bring forward a varied selection of these narratives. In a few cases, it will be seen, the subjects are, to say the least, on the borderland of the abnormal, but they do not come before us as patients desiring treatment. They are playing their, usually active, sometimes even distinguished, part in the world, which knows nothing of their intimate histories.