Unfortunately, however, we do not know the influence of racial cohesion. Obviously this is one of the fundamental points that ought to be known in order to gain a clear insight into the effect of recent immigration. Without this information, the whole discussion of the effect of intermixture remains speculative. The results of the present census will give us a certain amount of much-needed information on these points. In these remarks on the problems of European immigration I have confined myself entirely to the biological problem, because all our considerations have shown conclusively that mental life is so plastic, that no hereditary inability can be assumed to exist in any of the peoples of Europe. When we turn our attention to the negro problem as it presents itself in the United States, we must remember our previous considerations, in which we found that no proof of an inferiority of the negro type could be given, except that it seemed possible that perhaps the race would not produce quite so many men of highest genius as other races, while there was nothing at all that could be interpreted as suggesting any material difference in the mental capacity of the bulk of the negro population as compared to the bulk of the white population. Much has been said about the shorter period of growth of the negro child as compared to the white child, but no convincing data have been forthcoming. Considering the great variation in the duration of growth and development in different individuals and in various social classes, according to the more or less favorable nutrition of the child, the information that we possess in regard to the negro child is practically without value. We have not even evidence that would prove that a shorter period of development must be unfavorable in its results. Neither do we know at what period and in what manner develop the typical negroid features, which are much less pronounced in the new-born than in adults. It is surprising, that, notwithstanding their importance, no attempts have been made to gain a better insight into these anatomical and physiological problems, some of which might be solved without much difficulty. As it is, almost all we can say with certainty is, that the differences between the average types of the white and of the negro, that have a bearing upon vitality and mental ability, are much less than the individual variations in each race.