Pasteur’s proof that spontaneous generation does not occur in the solutions used by him does not prove that a synthesis of living from dead matter is impossible under any conditions. It is at least not inconceivable that in an earlier period of the earth’s history radio-activity, electrical discharges, and possibly also the action of volcanoes might have furnished the combination of circumstances under which living matter might have been formed. The staggering difficulties in imagining such a possibility are not merely on the chemical side--_e. g._, the production of proteins from CO₂, and N--but also on the physical side if the necessity of a definite cell structure is considered. We shall see in the sixth chapter that without a structure in the egg to begin with, no formation of a complicated organism is imaginable; and while a bacterium may have a simple structure, such a structure as it possesses is as necessary for its existence as are its enzymes. Attempts have repeatedly been made to imitate the structures in the cell and of living organisms by colloidal precipitates. It is needless to point out that such precipitates are of importance only for the study of the origin of structures in the living, but that they are not otherwise an imitation of the living since they are lacking the characteristic synthetic chemical processes. CHAPTER III THE CHEMICAL BASIS OF GENUS AND SPECIES 1. It is a truism that from an egg of a species an organism of this species only and of no other will arise. It is also a truism that the so-called protoplasm of an egg does not differ much from that of eggs of other species when looked at through a microscope. The question arises: What determines the species of the future organism? Is it a structure or a specific chemical or groups of chemicals? In a later chapter we shall show that the egg has a simple though definite structure, but in this chapter we shall see that the egg must contain specific substances and that these substances which determine the “species” and specificity in general are in all probability proteins. Since solutions of different proteins look alike under a microscope we need not wonder that it is impossible to discriminate microscopically between the protoplasm of different eggs.