Summing up the matter of insanity, the Commission speaks as follows: “For the high ratio of insanity among the foreign-born, several causes have been assigned, and while it is difficult to determine the values of the various factors it is probably true that racial traits or tendencies have a more or less important influence. A further cause of mental disease is probably to be found in the total change in climate, occupation, and habits of life which the majority of immigrants experience after arrival in the United States.” The efficiency of the inspection in regard to feeble-mindedness is shown by the very small proportion of foreign-born of that class appearing in the statistics. This is an affliction which can more easily be detected than the liability to insanity, of which there may be no observable indication at the time of admission.[306] CHAPTER XVI INDUSTRIAL EFFECTS. CRISES. SOCIAL STRATIFICATION. POLITICAL EFFECTS It has been observed already that the great argument for immigration during the past half century has been the economic one. The main defense for immigration has rested upon the claim that it has decidedly increased the industrial efficiency of the American people, and has facilitated the development of our resources, and the expansion of industry, at a rate which would not have been possible otherwise. The facts in regard to the age, sex, and physical soundness of the immigrants are mustered to establish them as a peculiarly efficient industrial body. This contention rests upon two assumptions. First, that our alien residents constitute a net addition to the total population of the country; second, that if there had been no immigration, and the population, particularly that part of it which constitutes the labor supply, had been smaller, that there would have been no inventions and improvements in the way of labor-saving machinery which would have permitted the same amount of work to be accomplished with a smaller amount of labor. In the light of what has been said in regard to the relation between immigration and the growth of population in Chapter XI, the first of these claims, at the very least, is open to serious question. While the proposition, as has already been stated, is absolutely incapable of mathematical proof, there nevertheless is every reason to believe that our immigrants have not meant a gain in the labor supply, but the substitution of one labor element for another. Not only have the immigrants in general displaced the natives, but the newer immigrants have displaced the older ones in a wide variety of industries and occupations. This latter process has gone on before our very eyes; it is manifest and perfectly comprehensible. A careful consideration of it may make it easier to understand how the same result, in a more subtle way, has been accomplished in the case of the native-born.