4. We are not concerned in this volume with the many applications of the theory of heredity to the breeding of plants, animals, and man; the reader will find a discussion of these topics in the numerous writings of the special workers on genetics.[208] We are, however, interested in the bearing this work has on the conception of the organism. Two questions present themselves: Is the organism nothing but a mosaic of hereditary characters determined essentially by definite elements located in the chromosomes; and if this be true, what makes a harmonious whole organism out of this kaleidoscopic assortment? We call it a kaleidoscopic assortment since a glance at the list of hereditary characters found in one chromosome, according to Morgan, shows that there is apparently no physiological or chemical connection between them, and second: How can a factor contained in the chromosome determine a hereditary character of the organism? To the first question we venture to offer the answer which has been already suggested in various chapters of this book, that the cytoplasm of the egg is the future embryo in the rough; and that the factors of heredity in the sperm only act by impressing the details upon the rough block. This metaphor will receive a more definite meaning by the answer to the second question. The characters which follow Mendelian heredity are morphological features as well as instincts. For the former we have already had occasion to show in previous chapters to what extent they depend upon the internal secretions or the existence of specific compounds in the circulation, and the same is true for the instincts (Chapters VIII and X). This then leads us to the suggestion that these determiners contained in the chromosomes give rise each to the formation of one or more specific substances which influence various parts of the body. We probably do not notice all the effects in each case, but when a special organ is affected in a conspicuous way, we connect the factor with this organ or the special feature of the organ which is altered, and speak of a determiner or factor for that organ, or for one of its characters. We also understand in this way why outside conditions should be able to overcome the hereditary tendency in certain cases, for instance why the influence of certain hereditary factors for pigmentation should depend upon temperature as E. Baur observed. [208] Bateson, W., _Mendel’s Principles of Heredity_, 3d ed., 1913; Davenport, Chas. B., _Heredity in Relation to Eugenics_, 1911. Pearl, R., _Modes of Research in Genetics_.