of this foam.  This conception is certainly not the prevalent one to-day; and even if it should be the proper one, it would still leave the cell as an extremely complicated machine.  Under any view the cell is a mechanism and must be resolved into subordinate parts.  It may be uncertain whether these subordinate parts are to be regarded simply as chemical compounds physically mixed, or as smaller units each of which is a smaller mechanism.  At all events, at the present time we know of no such simple protoplasm capable of living activities apart from machinery, and the problem of explaining life, even in the simplest form known, remains the problem of explaining a mechanism.

==The Origin of the Cell Machine.==—­We have thus set before us another problem, which is after all the fundamental one, namely, to ask whether we can tell anything of nature’s method of building the protoplasmic machine.  The building of the higher animal and plant, as we have seen, is the result of the powers of protoplasm; but protoplasm itself is a machine.  What has been its history?

We must first notice that no notion of chemical evolution helps us out.  It has been a favourite thought with some that the origin of the first living thing was the result of chemical evolution.  As the result of physical forces there was produced, from the original nebulous mass, a more and more complicated system until the world was formed.  Then chemical phenomena became more and more complicated until, with the production of more and more complicated compounds, protoplasm was finally produced.  A few years ago, under the impulse of the idea that protoplasm was a compound, or at least a simple mixture of compounds, this thought of protoplasm as the result of chemical evolution was quite significant. Physical forces, chemical forces, and vital forces, explain successively the origin of worlds, protoplasm, and organisms.  This conception has, however, no longer much significance.  We know of no such living chemical compound apart from cell machinery.  A new conception of protoplasm has arisen which demands a different explanation of its origin.  Since it is a machine rather than a compound, mechanical rather than chemical forces are required for its explanation.

Have we then any suggestion as to the method of the origin of this protoplasmic machine?  Our answer must, at the present, be certainly in the negative.  The complexity of the cell tells us plainly that it can not be the ultimate living substance which may have arisen from chemical evolution.  It is made up of parts delicately adapted to act in harmony with each other, and its activity depends upon the relation of these parts.  Whatever chemical forces may have accomplished, they never could have combined different bodies into linin, centrosomes, chromosomes, etc., which, as we have seen, are the basis of cell life.  To account for this machine, therefore,