"Far from endeavoring to obtain cross races, men who are occupied in raising stock, also bird-fanciers, know with what care they endeavor to preserve the purity of the races they keep. This is the general fact, and the result is, _that infecundity is the law of unions between animals belonging to different races_. "This is the fundamental distinction between _species_ and _race_. This distinction ought to be the more known and considered, as it is borrowed from experience. "When there are two animals, or two vegetables, of whom we are uncertain as to whether they are two distinct _species_, we have but to observe if their union is fruitful; and if this quality attaches to their descendants, we can then affirm that, despite the differences that separate them, _they are the races of the same species_. {74} If, on the contrary, their offspring diminishes in a remarkable manner at the end of several generations, we can then, without hesitation, declare them to belong to _distinct species_. In citing these examples, I have not overlooked the subject of my discourse, or the question at its commencement. "In referring to the designs before our eyes, they show us that between the human groups the differences are marked enough, though to all appearance less considerable than they appeared at first. We do not know the types, or the primitive types, of the several groups. "When we meet with one or several men presenting the characteristics of these types, and we cannot recognize them in spite of historical explanations, we are led to judge by our eyes. Without taking man himself into account, we cannot decide if these several differences that present themselves in the human family are those of _race_ or of _species_; if man can be considered as having had but one primitive source only, or if he should have been derived from several primitive sources. "I have said before, and repeat again, man is an organized and living being. Under this head he obeys all the general laws to which are attached all organized and living beings; he obeys, consequently, the law of crossing. He must then apply this law to ascertain _if there is one or several species of men_. Take, for example, the two types farthest removed--those which seem more separated than the others by the greatest differences--namely, the white and the black. "If these types really constitute _distinct species_, the union between these species should follow the proof that we have seen characterize the unions between animals, and vegetables, of different species. They should be unfruitful in the majority of cases, or nearly so. Fecundity should disappear at the end of a short period, and they could not form intermediate families between the negroes and the whites. If these are only _the races of one and the same species_, then unions, on the contrary, should be quite fruitful, and fecundity should be found among their descendants, and they should form intermediate races.