The differences between one and another of these three streams of population and the antagonisms which they have involved have greatly colored American history. The Indian, the European, and the Negro apparently differ not only in outward appearance but in the much more important matter of mentality. According to Brinton * the average brain capacity of Parisians, including adults of both sexes, is 1448 cubic centimeters. That of the American Indian is 1376, and that of the Negro 1344 cubic centimeters. With this difference in size there appears to be a corresponding difference in function. Thus far not enough accurate tests have been made upon Indians to enable us to draw reliable conclusions. The Negro, however, has been tested on an extensive scale. The results seem to leave little doubt that there are real and measurable differences in the mental powers of races, just as we know to be the case among individuals. The matter is so important that we may well dwell on it a moment before turning to the cause of the differences in the three streams of American immigrants. If there is a measurable difference between the inherent brain power of the white race and the black, it is practically certain that there are also measurable differences between the white and the red. * D. G. Brinton. "The American Race." Numerous tests indicate that in the lower mental powers there is no great difference between the black and the white. In physical reactions one is as quick as the other. In the capacity of the senses and in the power to perceive and to discriminate between different kinds of objects there is also practical equality. When it comes to the higher faculties, however, such as judgment, inventiveness, and the power of organization, a difference begins to be apparent. These, as Ferguson * says, are the traits that "divide mankind into the able and the mediocre, the brilliant and the dull, and they determine the progress of civilization more directly than do the simple fundamental powers which man has in common with the lower animals." On the basis of the most exhaustive study yet made, Ferguson believes that, apart from all differences due to home training and environment, the average intellectual power of the colored people of this country is only about three-fourths as great as that of white persons of the same amount of training. He believes it probable, indeed, that this estimate is too high rather than too low. As to the Indian, his past achievements and present condition indicate that intellectually he stands between the white man and the Negro in about the position that would be expected from the capacity of his brain. If this is so, the mental differences in the three streams of migration to America are fully as great as the outward and manifest physical differences and far more important. * G. O. Ferguson. "The Psychology of the Negro," New York, 1916.