Reproduction remains, which is the faculty most characteristic of life, and which distinguishes most sharply the organic from the inorganic world. In the inorganic there is no known process by which dead matter reproduces itself, as the cell does when it contracts in the middle and splits up into two cells, which in their turn propagate an endless number of similar cells, increasing in geometrical progression until they supply the raw material from which all the countless varieties of living organisms are built up, which, in their turn, repeat the process and reproduce themselves in offspring. This is the real mystery of life; we can partly see or suspect how its other faculties might arise from an extension of the known qualities and laws of matter and of energy; but we can discern no analogy between the non-reproductive nitrogenous carbon compound, which makes so near an approach to protoplasm in its chemical composition, and the reproductive protoplasm, which is fertile, increases and multiplies, and replenishes the earth. Can the gap be bridged over: can protoplasm be manufactured out of chemical elements? It is done every day by plants which make protoplasm out of inorganic elements, and by the lowest forms of life which live and multiply in chemical solutions. It is done also in the life-history of all individuals whose primitive cell or ovum makes thousands or millions of other cells, each containing within its enclosing membrane as much protoplasm as there was in the unit from which they started. But in all these instances there was the living principle to start with, existing in the primitive speck of protoplasm, from which the rest were developed. Can this primitive speck be created; or, in other words, can protoplasm be artificially manufactured by chemical processes?