The most careful study yet made of the relative intelligence of Negroes and whites is that of G. O. Ferguson, Jr.,[140] on 486 white and 421 colored pupils in the schools of Richmond, Fredericksburg, and Newport News, Va. Tests were employed which required the use of the "higher" functions, and as far as possible (mainly on the basis of skin-color) the amount of white blood in the colored pupils was determined. Four classes were made: full-blood Negro, 3/4 Negro, 1/2 Negro (mulatto) and 1/4 Negro (quadroon). It was found that "the pure Negroes scored 69.2% as high as the whites; that the 3/4 pure Negroes scored 73.2% as high as the whites; that the mulattoes scored 81.2% as high as the whites; and that the quadroons obtained 91.8% of the white score." This confirms the belief of many observers that the ability of a colored man is proportionate to the amount of white blood he has. Summarizing a large body of evidence, Dr. Ferguson concludes that "the intellectual performance of the general colored population is approximately 75% as efficient as that of the whites," but that pure Negroes have only 60% of white intellectual efficiency, and that even this figure is probably too high. "It seems as though the white type has attained a higher level of development, based upon the common elementary capacities, which the Negro has not reached to the same degree." "All of the experimental work which has been done has pointed to the same general conclusion." This is a conclusion of much definiteness and value, but it does not go as far as one might wish, for the deeper racial differences of impulse and inhibition, which are at present incapable of precise measurement, are likewise of great importance. And it is the common opinion that the Negro differs in such traits even more than in intellect proper. He is said to be lacking in that aggressive competitiveness which has been responsible for so much of the achievement of the Nordic race; it is alleged that his sexual impulses are strongly developed and inhibitions lacking; that he has "an instability of character, involving a lack of foresight, an improvidence, a lack of persistence, small power of serious initiative, a tendency to be content with immediate satisfactions." He appears to be more gregarious but less apt at organization than most races.