6 THE POPULAR SCIENCE MONTHLY. 



Even in the highest animals there remains traceable this relation be- 

 tween 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 tbem, then known as a white corpuscle, 

 makes independent movements like those of an amoeba ; 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 essen- 

 tially 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 ag- 

 gregate has a further character common to the two cases. By a ca- 

 tastrophe the life of the aggregate may be destroyed without imme- 

 diately 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 coordinations, etc., which constitute the 

 corporate life of a nation, may be caused, say by an inroad of bar- 

 barians, 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, 



