Organization now took the direction of increasing specialization, and the higher the organism the more limited is the sphere of duty of each cell. It has gone to such an extreme that the cell-citizens of the bodies of mammals are so specialized that each can do but one little thing. Division of labor has reached an extreme undreamed of in any modern factory, for the cell-citizen has become so specialized as to be absolutely unable to do anything except his own little work. He may act as a fish scale on the skin to protect mechanically by his body; he may be transparent in the cornea; he may contract in muscle or give out a peculiar form of energy in a nerve cell. We now have a perfect picture of commensalism or mutual aid. Each cell works for the community while working for itself. It is fed, protected and cared for simply because it is needed by the commonwealth. A cell is even protected and fed long after the community, by change of habits, has no further use for its special duty. Thus the vermiform appendix and other vestiges of former useful parts are retained for thousands of generations after they cease to be useful. It is the law of organic inertia. Similarly, society retains many units long after their usefulness ends - criminals, insane and paupers - but this is a result of the necessity of making life safe for every one. But the community has no hesitation in sacrificing citizens when the occasion arises. When enemies (bacteria) invade the society, the soldiers or leucocytes hurl themselves in vast armies to combat the invaders - actually eating the enemies alive. Uncounted numbers of leucocytes perish in this battle - an abscess is a mass of their dead bodies. They have sacrificed themselves, like Japanese soldiers, to save the commonwealth. In like manner, parts are sloughed off en masse, when they become deleterious or when it is otherwise necessary.
Control is absolutely necessary or the cells would run riot. A cancer, for instance, is a mass of cells which have escaped control, though of course we do not yet know why. The disease is the result of lawlessness. There are certain citizens, the nerve cells, which have been born to guide, direct and rule, as their ancestors have done from time immemorial, even back to the time when they were part of the surface or protective layer. The brain and spinal cord are merely infolded parts of the skin. These citizens have the ruling divided up among them in a specialized way. Some control all the transportation systems, others constitute a signal corps, and some of these are in a telegraph exchange, others in a telephone service, others in the telescope service, others preside over signals set up by waves called odors and tastes, other sets of cells manage the factory operatives of various glands such as the liver, parotid or stomach, carefully regulating the amount of finished product according to the common needs. Other citizens attend to the heating apparatus and the power plant, others look after ventilation (breathing), or the circulation of goods in pipe lines like the Standard Oil Trust, and others attend to sewage. These are all ruling and guiding citizens who never do any productive work at all. They are like the staff of an army, and are all more or less controlled, coordinated and directed in their work by the higher brain-cells whose functions we call the "will" - the general in command. Some are quite independent of the will and are said to be involuntary in their action, nevertheless they are under control of some sort.
There is nothing like a caste system in this socialism. Each cell, to be sure, is confined to its hereditary calling, and some sets are vastly more important than others. An arm can be cut off and the organism survive, but the destruction of a few brain cells might be fatal. Consequently, some citizens are given better protection than others, and more food. The blood supply to the head is enormous, as compared to that given to the feet. But the caste system is absent in that each citizen is on an equality as to its needs. It is a true democracy in which very few citizens possess the franchise or direction of affairs, and yet nearly all have some share in creating what might be called public opinion - the mind.