There is only one exception to this rule. In all cases in which the anthropometric traits undergo very considerable changes during the period of growth, the influence of favorable or unfavorable causes makes itself felt. The investigations conducted by Gould and Baxter during the war of the Rebellion have shown that the representatives of European nationalities born in America have statures higher than the representatives of the same nationalities born in Europe; and it has been assumed that better nutrition, or perhaps better hygienic and economic conditions in general, might increase the stature of a people. These conclusions were confirmed by Bowditch’s measurements of the school-children of Boston, and by Peckham’s anthropometric work in Milwaukee. These changes in stature, due to changed conditions, have recently been demonstrated also in Europe, where Ammon has shown that the population of Baden has materially increased in size during the last thirty years. Other corroborative evidence has been obtained from the study of various social classes, in which Bowditch found an increase of stature, beginning with the children of unskilled laborers, and increasing among those of skilled laborers, members of the mercantile class and of the professional class; and from the observations showing a correlation between the character of streets occupied by the well-to-do and the poor, and the stature of their inhabitants (Ripley). Nevertheless these changes of stature were not interpreted as changes in type, because they may well be understood to be due to the elimination of retarding influences, which prevent many individuals from attaining their normal growth. The results of the observations on stature are substantiated by other anthropometrical studies of various occupations. The best-authenticated fact, because based on the greatest number of observations, is the difference in type between sailors and soldiers who were measured during the war of the Rebellion. It was found that sailors had legs as long as those of the negroes, and correspondingly a shorter trunk, while their arms were equally as long as those of the soldiers of the army. We may also call to mind the investigations carried on in the gymnasiums of our colleges, which show that a series of measurements which depend largely upon the functions of groups of muscles change very rapidly under the influence of practice. It will be acknowledged at once that differences in the use of muscles during childhood, and continued in later life, must result in differences of structure, either permanent, or at least temporary.