Rolph thinks Spencer's theory awakes the conjecture that it was not first arrived at through investigation, but rests upon a preconceived opinion, as do to a greater or less extent all theories on this subject. It seems as if the author had first attached himself to that theory which best accorded with his scientific bias, and then tried whether this theory might be proved or supported by facts of biology and psychology. One might surmise, from the very skilful, but often too artificial argument, that the author pursued the following train of thought. Pleasure, and indeed the greatest possible pleasure, is the end of endeavor in the organic world, that is, the psychical cause of endeavor. May it not also be the physical cause? Rolph answers this question with a denial, and endeavors to show that the taking of food has its cause in the insatiability of all organic substance. The theory of Spontaneous Generation contains nothing impossible or improbable; is, on the contrary, a necessary logical assumption not to be disproved by the mere result of experiment under conditions of the laboratory. It is easy to imagine that organic elements, which are to be found in great quantities in inorganic nature, may come together by chance, or rather in the natural order of things, to the formation of protoplasm. The movement of these masses of protoplasm seems, at first glance, to set the law of gravitation at defiance, but we may answer that an ascending balloon might seem, to an uninstructed observer, to do the same, although its movement is merely the natural result of that force; it is not necessary, therefore, to assume a free inner motive, the soul, as the cause of the one motion or the other. The first assimilation of food has its beginning in the process of endosmose and exosmose, in which the protoplasm, as in general the denser fluid, increases in volume, taking up more than it gives out; the process occurring, in detail, according to the special relations of attraction in the parts. The organism always takes up the greatest amount possible under the circumstances, exactly as, in the inorganic world, water takes up the greatest amount possible of salt or any other soluble substance; the growth of a crystal, and the oxidation of iron are illustrations of the same principle. Of the limit of this capacity to take up new matter into the organism we know nothing; all recent experiments go to show that the organism is capable, under propitious circumstances, of an enormous receptivity, such as, under natural conditions, it never reaches. The lower animals feed continually, and their whole lives are passed in this employment. In plants the tendency is seen still more clearly. Experiments with electric, violet, and ultra-violet light show an enormous growth in plants exposed to its action. But this can be only an indirect growth, namely, the exorbitant acceleration of organic change and assimilation. This fact is proved by experiments turning on increase