difference between the growth of an organism and that of a crystal is, that in the former case, in consequence of its semi-fluid state of aggregation, the newly added particles penetrate into the interior of the organism (inter-susception), whereas inorganic substances receive homogeneous matter from without, only by opposition or an addition of new particles to the surface. "If we, then, designate the growth and the formation of organisms as a process of life, we may with equal reason apply the same term with the developing crystal." It is for these and other reasons, demonstrating as they do the "unity of organic and inorganic nature," the essential agreement of inorganic and organic bodies in matter, form, and force, which led Tyndall[14] to say: "Abandoning all disguise, the confession that I feel bound to make before you is, that I prolong the vision backward across the boundary of experimental evidence, and discern in that matter which we in our ignorance, and notwithstanding our professed reverence for its Creator, have hitherto covered with opprobrium, the promise and potency of every form and quality of life." Returning now to our protoplasm, let us ask the question: Where did it come from? or, How did it come into existence? Though chemical synthesis has built up a number of organic substances which have been deemed the product of vitality, yet, up to the present day, the fact stands out before us that no one has ever built up one particle of living matter, however minute, from lifeless elements. The protoplasm of to-day is simply a continuation of the protoplasm of other ages, handed down to us through periods of undefinable and indeterminable time. The question of where protoplasm came from--how it arose--chemistry is unable to answer; but the question is answered, probably, by spontaneous generation. Only the merest particle of living protoplasm was necessary to be formed from lifeless matter in the beginning; for, in the eyes of any consistent evolutionist, any further independent formation would be sheer waste, as the hypothesis of evolution postulates the unlimited, though perhaps not, indefinite modifiability of such matter. As we have seen that there exists no absolute barrier between organic and inorganic bodies, it is not so difficult to conceive that the first particle of protoplasm may have originated, under suitable conditions, out of inorganic or lifeless matter. But the causes which have led to the origination of this particle, it may be said, we know absolutely nothing--as in the formation of the crystal and the cell--the ultimate causes remain in both cases concealed from us.