Page:Popular Science Monthly Volume 13.djvu/697

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T has been shown in former articles that living motion is the result of alternate expansion and contraction on the part of the protoplasm; and we could not fail to perceive that this occupation of so much more or so much less space is the physical property of the protoplasm under different states of chemical composition. It remains to be ascertained by what agencies the chemical composition and decomposition of the living substance are affected. What are the influences that disintegrate the protoplasm? and what are the influences that reintegrate it?

A little attention to the visible changes which occur in the expanding material of different monera, when being checked in its onward course, soon demonstrates that it is the resistance of the medium, the counteraction of the energies composing the immediate environment, which causes chemical rupture in the organic substance. The molecule of protoplasm, like all very high compounds, and, in fact, like almost all nitrogenous compounds, is in a considerable degree explosive. During the expansion of the protoplasm, the medium is pushing against it with a force of its own; and it is this opposing energy, exerted by the medium, which, at some definite moment of its increasing composition and consequent expansion, causes this living substance at last to explode.

No unscientific conjecture has been allowed to enter into the above conception of this highly-important vital occurrence. It is as a mental sketch, in its outline, as positive and certain as any fact of Nature can possibly be.

In observing this process of decomposition, first the outer envelope of the projecting cone is seen to become disintegrated, and, in lower monera, also solidified. In these lower specimens the expanding material pushes still onward along the central axis of the cone, breaking through its apex, until it is at last also overcome by rigidity.

As the expanding material is perfectly translucent, the slightest optical change in it can be easily detected. The whitish, somewhat more opaque appearance of the stagnating protoplasm indicates that an important molecular alteration has taken place. That this alteration is of a chemical nature is actually proved by the products of decomposition being in many instances visibly gathered into a separate globule.

Thus the dynamical energy of the medium applies the match, gives the turning-stroke to the pending explosion, and it is by this