It is useless to try to go further at present.  The origin of living matter is shrouded in as great obscurity as ever.  We must admit that the disclosures of the modern microscope have complicated rather than simplified this problem.  While a few years ago chemists and biologists were eagerly expecting to discover a method of manufacturing a bit of living matter by artificial means, that hope has now been practically abandoned.  The task is apparently hopeless.  We can manipulate chemical forces and produce an endless series of chemical compounds.  But we can not manipulate the minute bits of matter which make up the living machine.  Since living matter is made of the adjustment of these microscopic parts of matter, we can not hope to make a bit of living matter until we find some way of making these little parts and adjusting them together.  Most students of protoplasm have therefore abandoned all expectation of making even the simplest living thing.  We are apparently as far from the real goal of a natural explanation of life as we were before the discovery of protoplasm.

==General Summary.==—­It is now desirable to close this discussion of seemingly somewhat unconnected topics by bringing them together in a brief summary.  This will enable us to see more clearly the position in which science stands to-day upon this matter of the natural explanation of living phenomena, and to picture to ourselves more concisely our knowledge of the living machine.

The problem we have set before us is to find out to what extent it is possible to account for vital phenomena by the application of ordinary natural laws and forces, and therefore to find out whether it is necessary to assume that there are forces needed to explain life which are different from those found in other realms of nature, or whether vital forces are all correlated with physical forces.  It has been evident at a glance that the living body is a machine.  Like other machines it consists of parts adjusted to each other for the accomplishment of definite ends, and its action depends upon the adjustment of its parts.  Like other machines, it neither creates nor destroys energy, but simply converts the potential energy of its foods into some form of active energy, and, like other machines, its power ceases when the machine is broken.

With this understanding the problem clearly resolved itself into two separate ones.  The first was to determine to what extent known physical and chemical laws and forces are adequate to an explanation of the various phenomena of life.  The second was to determine whether there are any known forces which can furnish a natural explanation of the origin of the living machine.  Manifestly, if the first of these problems is insolvable, the second is insolvable also.