a psychic force—­all distinctions which we cannot well dispense with, though of the ultimate reality for which these terms stand we can know little.  In the latest science heat and light are not substances, though electricity is.  They are peculiar motions in matter which give rise to sensations in certain living bodies that we name light and heat, as another peculiar motion in matter gives rise to a sensation we call sound.  Life is another kind of motion in certain aggregates of matter—­more mysterious or inexplicable than all others because it cannot be described in terms of the others, and because it defies the art and science of man to reproduce.

Though the concepts “vital force” and “life principle” have no standing in the court of modern biological science, it is interesting to observe how often recourse is had by biological writers to terms that embody the same idea.  Thus the German physiologist Verworn, the determined enemy of the old conception of life, in his great work on “Irritability,” has recourse to “the specific energy of living substances.”  One is forced to believe that without this “specific energy” his “living substances” would never have arisen out of the non-living.

Professor Moore, of Liverpool University, as I have already pointed out while discussing the term “vital force,” invents a new phrase, “biotic energy,” to explain the same phenomena.  Surely a force by any other name is no more and no less potent.  Both Verworn and Moore feel the need, as we all do, of some term, or terms, by which to explain that activity in matter which we call vital.  Other writers have referred to “a peculiar power of synthesis” in plants and animals, which the inanimate forms do not possess.

Ray Lankester, to whom I have already referred in discussing this subject, helps himself out by inventing, not a new force, but a new substance in which he fancies “resides the peculiar property of living matter.”  He calls this hypothetical substance “plasmogen,” and thinks of it as an ultimate chemical compound hidden in protoplasm.  Has this “ultimate molecule of life” any more scientific or philosophical validity than the old conception of a vital force?  It looks very much like another name for the same thing—­an attempt to give the mind something to take hold of in dealing with the mystery of living things.  This imaginary “life-stuff” of the British scientist is entirely beyond the reach of chemical analysis; no man has ever seen it or proved its existence.  In fact it is simply an invention of Ray Lankester to fill a break in the sequence of observed phenomena.  Something seems to possess the power of starting or kindling that organizing activity in a living body, and it seems to me it matters little whether we call it “plasmogen,” or a “life principle,” or “biotic energy,” or what not; it surely leavens the loaf.  Matter takes on new activities under its influence.  Ray Lankester thinks that plasmogen came into being in early geologic ages, and that the conditions which led to its formation have probably never recurred.  Whether he thinks its formation was merely a chance hit or not, he does not say.