This is the fundamental idea in Goethe’s “Wahlverwandtschaften” (Elective Affinities), and in the fourth chapter of the first part of that work he makes it the subject of a playful introduction which was full of undreamed of future significance, and the full force of which he was fated himself to experience in later life. I must confess to being proud that this book is the first work to take up his ideas. None the less, it is as little my intention as it was the intention of Goethe to advocate divorce; I hope only to explain it. There are human motives which indispose man to divorce and enable him to withstand it. This I shall discuss later on. The physical side of sex in man is less completely ruled by natural law than is the case with lower animals. We get an indication of this in the fact that man is sexual throughout the year, and that in him there is less trace than even in domestic animals of the existence of a special spring breeding-season. The law of sexual affinity is analogous in another respect to a well-known law of theoretical chemistry, although, indeed, there are marked differences. The violence of a chemical reaction is proportionate to the mass of the substances involved, as, for instance, a stronger acid solution unites with a stronger basic solution with greater avidity, just as in the case of the union of a pair of living beings with strong maleness and femaleness. But there is an essential difference between the living process and the reaction of the lifeless chemical substances. The living organism is not homogeneous and isotropic in its composition; it is not divisible into a number of small parts of identical properties. The difference depends on the principle of individuality, on the fact that every living thing is an individual, and that its individuality is essentially structural. And so in the vital process it is not as in inorganic chemistry; there is no possibility of a larger proportion forming one compound, a smaller proportion forming another. The organic chemotropism, moreover, may be negative. In certain cases the value of A may result in a negative quantity, that is to say, the sexual attraction may appear in the form of sexual repulsion. It is true that in purely chemical processes the same reaction may take place at different rates. Taking, however, the total failure of some reaction by catalytic interference as the equivalent of a sexual repulsion, it never happens, according to the latest investigations at least, that the interference merely induces the reaction after a longer or shorter interval. On the other hand, it happens frequently that a compound which is formed at one temperature breaks up at another temperature. Here the “direction” of the reaction is a function of the temperature, as, in the vital process, it may be a function of time.