Even in the highest animals there remains traceable this relation between the aggregate life and the lives of components. Blood is a liquid in which, along with nutritive matters, circulate innumerable living units—the blood-corpuscles. These have severally their life-histories. During its first stage each of them, then known as a white corpuscle, makes independent movements like those of an amœba; and though in its adult stage, as a red, flattened disk, it is not visibly active, its individual life continues. Nor is this individual life of the units provable only where free flotation in a liquid allows its signs to be readily seen. Sundry mucous surfaces, as those of the air-passages, are covered with what is called ciliated epithelium—a layer of minute cells packed side by side, and each bearing on its exposed end several cilia continually in motion. The wavings of these cilia are essentially like those of the monads which live in the passages running through a sponge; and just as the joint action of these ciliated sponge monads propels the current of water, so does the joint action of the ciliated epithelium-cells move forward the mucous secretion covering them. If there needs further proof of the individual lives of these epithelium-cells, we have it in the fact that, when detached and placed in fluid, they "move about with considerable rapidity for some time, by the continued vibrations of the cilia with which they are furnished."
On thus seeing that an ordinary living organism may be regarded as a nation of units that live individually, and have many of them considerable degrees of independence, we shall perceive how truly a nation of human beings may be regarded as an organism.
The relation between the hives of the units and the life of the aggregate has a further character common to the two cases. By a catastrophe the life of the aggregate may be destroyed without immediately destroying the lives of all its units; while, on the other hand, if no catastrophe abridges it, the life of the aggregate immensely exceeds in length the lives of its units.
In a cold-blooded animal, ciliated cells perform their motions with perfect regularity long after the creature they are part of has become motionless; muscular fibres retain their power of contracting under stimulation; the cells of secreting organs go on pouring out their product if blood is artificially supplied to them; and the components of an entire organ, as the heart, continue their cooperation for many hours after its detachment. Similarly, arrest of those commercial activities and governmental coördinations, etc., which constitute the corporate life of a nation, may be caused, say by an inroad of barbarians, without immediately stopping the actions of all the units. Certain classes of these, especially the widely-diffused ones engaged in food-production, may, in the remoter districts, long survive and carry on their individual occupations.
Conversely, in both cases, if not brought to a close by violence,
