y of nature, and the study of the
psychology of man in health and in disease.

To harmonize the aspirations of human nature and the data of the
sociology of the different human races and the different epochs of
history, with the results of natural science and the laws of mental
and sexual evolution which these have revealed to us, is a task which
has become more and more necessary at the present day. It is our duty
to our descendants to contribute as far as is in our power to its
accomplishment. In recognition of the immense progress of education
which we owe to the sweat, the blood, and often to the martyrdom of
our predecessors, it behoves us to prepare for our children a life
more happy than ours.

I am well aware of the disproportion which exists between the
magnitude of my task and the imperfections of my work. I have not been
able to study as much as should be done the innumerable works which
treat of the same subject. Others, better versed than myself in the
literature of the subject, will be able later on to fill this
regrettable lacuna. I have endeavored, above all things, to study the
question from all points of view, in order to avoid the errors which
result from any study which is made from one point of view only. This
is a thing which has generally been neglected.

I must express my thanks to my friend, _Professor Mahaim_, and
especially to my publisher and cousin, _S. Steinheil_, for the help
and excellent advice which they have given me in the revision of my
work; also to _Professor Boveri_, who has been kind enough to revise
the figures, 1 to 17.

DR. A. FOREL.

Chigny pres Morges (Suisse).

PREFACE TO THE SECOND EDITION

The text of the first edition has been revised and corrected, but,
apart from some points of detail, the subject matter has not been
changed. The examples at the end of Chapter V (First Edition) no
longer form a special appendix; they have been included in the parts
of the book which specially concern them; some of them have been
omitted as being superfluous.

In the domain with which we are concerned the French public are too
much afraid, I think, of crudities and of calling things by their
proper name. By veiled words and by indirect locution one may say
anything, but I have decided not to employ such subterfuges in
treating of such a vital social question with the seriousness that it
requires. It seems that there