up of energy, but a transformation, a remolding of it in other and, in the case under consideration, higher kinds. As the wide and rapid vibrations which constitute the expansive power of steam are made, by means of suitable mechanical appliances, to disappear in condensation and to reappear as locomotion, so the potential forces locked up in the molecules of protoplasm appear in the breaking down, the decomposition, of these molecules as spontaneous movements of some portions of the mass.
The energy expended in the movements of protoplasm is supplied through the chemical changes going on in its substance, by the breaking down of compounds possessing much latent energy into more simple ones containing less such energy.
These downward chemical changes are mainly processes of oxidation, one of the chief products of oxidation being carbonic-acid gas. Now, the taking in of oxygen and the giving out of carbonic acid together constitute respiration; hence protoplasm is "respiratory"—another of its vital properties. It breathes, as the fish does, by absorption of oxygen from its surrounding medium; but it breathes at the entire surface of its mass instead of at special parts of its surface, as in the fish. This is true of vegetable as well as animal protoplasm, the two being indeed regarded, in all essential points, as identical.
Protoplasm is also "reproductive." Haeckel, in his history of the discovery of the monera, which consist of little globules of simple protoplasm, describes their mode of reproduction as follows: "The little creature divides into two halves, and each of these goes on living like the original one."
But there is a form of living protoplasm even more simple, if possible, than the moneron of Professor Haeckel—the Myxomycetæ—of which a very good description may be found in the inaugural address of Professor Allman, President of the British Association, in 1879, published in the October number of "The Popular Science Monthly" of that year. These organisms consist, during the greater part of their lives, of simple protoplasm. They may be found in moist places growing on decaying leaves, rotten wood, etc., etc., over which they spread in the form of a net-work, exhibiting amœboid movements, appearing to be sensitive to the light, and giving other evidences of life.
But we may find a specimen of protoplasm even nearer home than this. Prick your own fingers, if you choose; withdraw a drop of living blood from the wound, and, having properly diluted it, place it under your own microscope for observation. Scattered among the numerous small bodies which give to the blood its brilliant crimson hue, may be seen a few somewhat larger colorless ones—the leucocytes or white cells.
These microscopic bodies consist mainly of simple, undifferentiated protoplasm. They* differ from the monera (first found by Haeckel floating on the surface of the Mediterranean Sea) in being nucleated;