Without venturing, therefore, to speculate on the origin of the primitive cell, or unit of organic life, which involves the problem of the metamorphosis of a rude mass--the primitive transformation of the rudimentary atoms into organic form,--we must admit that the highly organized plant or animal is but an aggregation of cells; their arrangement being dependent upon certain properties peculiar to them, and the exercise of forces such as we have been studying,--all of which appear to act externally to the plant or animal itself. Experiments have been brought forward, in which it appeared that, after all organization which could by any possibility have existed, had been destroyed by the action of fire, solutions of flint and metallic salts, have, under the influence of electric currents, exhibited signs of organic formations, and that, indeed, insects--a species of acari--have been developed in them. The experiments were said to have been made with care, and many precautions taken to shut out all chances of any error, but not all the precautions required in a matter of such exceeding delicacy; and we are bound not to receive the evidence afforded as the true expression of a fact without much further investigation. All experience,--setting aside the experiment named,--is against the supposition that pounded or dissolved flint could by any artificial means be awakened into life. Ova may have been conveyed into the vessels which contained the solutions under experiment; and in due time, although possibly quickened by electric excitation, the animals--the most common of insects--came into existence.[255] The rapid growth of confervæ upon water has often been brought forward as evidence of a spontaneous generation, or the conversion of inorganic elements into organic forms; but it has been most satisfactorily proved that the germ must be present, otherwise no evidence of anything like organization will be developed. All the conditions required for the production of vegetable life appear to show, that it is quite impossible for any kind of plant, even the very lowest in the scale, to be formed in any other way than from an embryo in which are contained the elements necessary for it, and the arrangements required for the various processes which are connected with its vitality. The earth is now covered with vegetable life, but there must have existed a time when “darkness was upon the face of the deep,” and organization had not yet commenced tracing its lovely net-work of cells upon the bare surface of the ocean-buried rock. At length the mystery of organic creation began: into this science dares not penetrate, but it is privileged to begin its search a little beyond this point, and we are enabled to trace the progress of organic development through a chain of interesting results which are constantly recurring.