The importance of this newly formulated doctrine it is difficult to appreciate.  Here, in protoplasm had been apparently found the foundation of living phenomena.  Here was a substance universally present in animals and plants, simple and uniform—­a substance always present in living parts and disappearing with death.  It was the simplest thing that had life, and indeed the only thing that had life, for there is no life outside of cells and protoplasm.  But simple as it was it had all the fundamental properties of living things—­irritability, contractibility, assimilation, and reproduction.  It was a compound which seemingly deserved the name of “physical basis of life”, which was soon given to it by Huxley.  With this conception of protoplasm as the physical basis of life the problems connected with the study of life became more simplified.  In order to study the nature of life it was no longer necessary to study the confusing mass of complex organs disclosed to us by animals and plants, or even the somewhat less confusing structures shown by individual cells.  Even the simple cell has several separate parts capable of undergoing great modifications in different types of animals.  This confusion now appeared to vanish, for only one thing was found to be alive, and that was apparently very simple.  But that substance exhibited all the properties of life.  It moved, it could grow, and reproduce itself, so that it was necessary only to explain this substance and life would be explained.

(b) Nature of Protoplasm.—­What is this material, protoplasm?  As disclosed by the early microscope it appeared to be nothing more than a simple mass of jelly, usually transparent, more or less consistent, sometimes being quite fluid, and at others more solid.  Structure it appeared to have none.  Its chief peculiarity, so far as physical characters were concerned, was a wonderful and never-ceasing activity.  This jellylike material appeared to be endowed with wonderful powers, and yet neither physical nor microscopical study revealed at first anything more than a uniform homogeneous mass of jelly.  Chemical study of the same substance was of no less interest than the microscopical study.  Of course it was no easy matter to collect this protoplasm in sufficient quantity and pure enough to make a careful analysis.  The difficulties were in time, however, overcome, and chemical study showed protoplasm to be a proteid, related to other proteids like albumen, but one which was more complex than any other known.  It was for a long time looked upon by many as a single definite chemical compound, and attempts were made to determine its chemical formula.  Such an analysis indicated a molecule made up of several hundred atoms.  Chemists did not, however, look with much confidence upon these results, and it is not surprising that there was no very close agreement among them as to the number of atoms in this supposed complex molecule.  Moreover, from the very first, some biologists thought