Can it be believed, then, that protoplasm, as the origin of life, is self-caused, and self-developed?  And this is not all.  I must briefly remind my readers that the way in which animal protoplasm deals with the elements of nutrition is quite opposite to that which plant protoplasm follows.  I might, indeed, have mentioned this at an earlier stage, when I mentioned Professor Huxley’s comparison of the chemical action in the formation of water with what he assumed to be the case in the formation of protoplasm.  When water is formed, the two gases disappear, and an exactly equal weight of water appears in their place; but if living protoplasm is enabled to imbibe liquid or other nutriment containing ammonia, water, and carbonic acid, there is no disappearance of the three elements and an equivalent weight of living protoplasm appearing in its place.  Protoplasm consumes the oxygen and sets free the carbonic acid.  Both kinds of protoplasm do this, until exposed to the light; and then a difference is observed; for under the influence of light, animal protoplasm alone continues to act in this way, and vegetable protoplasm begins at once to develop little green bodies or corpuscles in its cells, and afterwards acts in a totally opposite way, taking the carbon into its substance and giving off the oxygen.[1]

[Footnote 1:  Certain fungi seem to afford an exception to this.  The above is, I believe, true as a theoretical action of plants and animals in protoplasmic form.  But practically, in all higher developments of either kind, other distinctions come into play; e.g., that plants can make use of inorganic matter, gases, and water, and elaborate them into organic matter.  Animals cannot do this, they require more or less solid food—­always requiring “complex organic bodies which they ultimately reduce to much simpler inorganic bodies.  They are thus mediately or immediately dependent on plants for their subsistence” (Nicholson, “Zoology,” 6th ed. p. 17).  It is perhaps with reference to this that in the Book of Genesis the Creator is represented as giving plant life to the service of man and animals—­while nothing is said of the preying of Carnivora and Insectivora on animal life.]

Not only then has each kind of protoplasm its own mysterious character impressed on it, and is compelled to act in a certain way; but still further, each particle of animal and vegetable protoplasm, when directed into its general course of development as plant or animal, will again only obey a certain course of development in its own line.