rids
between themselves, but these hybrids are as a rule sterile or nearly
so, and are incapable of perpetuating their type, which reverts
rapidly to one of the primitive species.

It has been recently demonstrated that the incapacity of two species
of animals to produce hybrids is intimately connected with the
reciprocal toxicity of their blood. When the blood of one species is
injected into the veins of another the production of hybrids is
possible between them, at least as far as has been observed. It is
curious to note that the blood of the anthropoid apes is not toxic for
man, although these animals are very different from us, and hybrids
have not yet been produced. This fact helps us to understand how it is
that the differences which exist between the different human races do
not prevent the production of hybrids between any two of them. In
spite of this we may state, without risk of error, that the most
dissimilar human races give a bad quality of hybrids, which have
little chance of forming a viable mongrel race. We have not
sufficient information on this point concerning the lowest human
races, such as the pigmies and Weddas. On the other hand, mulattoes
(hybrids between negroes and whites) constitute a race of very bad
quality and hardly viable, while the hybrids between Indians and
whites are much more resistant and of relatively better quality.

In this question, the middle course appears without any doubt the true
one. Unions between near races and varieties, or at least between
individuals of the same race or variety whose relationship is old, are
certainly the best. We readily grant that the homogeneity of a race
has the advantage of fixing its peculiarities in a more durable and
characteristic fashion; but many inconveniences counterbalance this
advantage. If we one day, by wise selection and by eliminating all
sources of blastophthoria obtain a superior quality of human germs, it
is possible that in the remote future, consanguinity, provided it is
not exaggerated may lose its dangers.

CHAPTER III

NATURAL CONDITIONS AND MECHANISM OF HUMAN
COITUS--PREGNANCY--CORRELATIVE SEXUAL CHARACTERS

It is impossible to comprehend the deep meaning and lofty aim of an
act like that of sexual union without knowing the details of
conjugation and the origin of man as we have explained them in the
preceding chapters.

Conjugation requires the bringing together of two cells, and
consequently the movement