Page:A Text-book of Animal Physiology.djvu/63

Rh This, too, is primarily a molecular effect. If the works of watches were beyond observation, we should not be able to state exactly how the variations observed in different kinds, or even different individuals of the same kind occurred, though these differences might be of the most marked character, such as any one could recognize. Here once more we refer the differences to the mechanism. So is it with living beings: the ultimate molecular mechanism is unknown to us.

Could we but render these molecular movements visible to our eyes, we should have a revelation of far greater scientific importance than that unfolded by the recent researches into those living forms of extreme minuteness that swarm everywhere as dust in a sunbeam, and, as will be learned later, are often the source of deadly disease. Like the movements of the watch, the activities of protoplasm are ceaseless. A watch that will not run is, as such, worthless—it is mere metal—has undergone an immense degradation in the scale of values; so protoplasm is no longer protoplasm when its peculiar molecular movements cease; it is at once degraded to the rank of dead matter.

The student may observe that each of the four propositions, embodying the fundamental properties of living matter, stated in the preceding chapter, have been illustrated by the simile of a watch. Such an illustration is necessarily crude, but it helps one to realize the meaning of truths which gather force with each living form studied if regarded aright; and it is upon the realization of truth that mental growth as well as practical efficiency depends.

There are human beings so low in the scale as not to possess such general terms as tree, while they do employ names for different kinds of trees. The use of such a word as "tree" implies generalization, or the abstraction of a set of qualities from the things in which they reside, and making them the basis for the grouping of a multitude of objects by which we are surrounded. Manifestly without such a process knowledge must be very limited, and the world without significance; while in proportion as generalization may be safely widened, is our progress in the unification of knowledge toward which science is tending. But it also follows that without complete