It is thus clearly apparent that the phenomena of life are dependent upon the machinery of living things, and we have therefore the second question of the _origin_ of this machinery to answer. Chemical forces and mechanical forces have been laboriously investigated, but neither appear adequate to the manufacture of machines. They produce only chemical compounds and worlds with their mountains and seas. The construction of artificial machines has demanded intelligence. But here is a natural machine--the organism. It is the only machine produced by natural methods, so far as we know; and we have therefore next asked whether there are, in nature, simple forces competent to build machines such as living animals and plants? In pursuance of this question we have found that the complicated machines have been built out of the simpler ones by the action of known forces and laws. The factors in this machine building are simply those of the fundamental vital properties of the simplest protoplasmic machine. Reproduction, heredity, and variation, acting under the ever-changing conditions of the earth's surface, are apparently all that are needed to explain the building of the complex machines out of the simpler ones. Nature _has_ forces adequate to the building of machines as well as forces adequate to the formation of chemical compounds and worlds. But here again we are unable to base our explanation upon chemical and physical forces. Reproduction, heredity, and variation are properties of the cell machine, and we are therefore thrown back upon the necessity of explaining the origin of this machine. Can we find a mechanical or chemical explanation of the origin of protoplasm? A chemical explanation of the cell is impossible, since it is not a chemical compound, but a piece of mechanism. The explanation given for the origin of animals and plants is also here apparently impossible. The factors upon which that explanation depended are factors of this completed machine itself, and can not be used to explain its origin. We are left at present therefore without any foundation for further advance. The cells must have had a history of construction, but we do not as yet conceive any forces which may be looked upon as contributing to that history. Whether life phenomena can be manifested by any mixture of compounds simpler than the cell we do not yet know.