Harmony and Conflict in the Living World - Alexander F. Skutch [5]
With the exceptions of parasites and their hosts, only exceptionally do separate organisms unite as intimately as lifeless sub-
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stances so frequently do, and these are nearly always members of the same species. Relatively simple animalcules, like corals and sponges, join in large numbers to form compound organisms. Roots of different trees of the same species, especially conifers, may fuse together when they meet in the soil, and the horticulturist's art may graft one variety of a tree or shrub upon the stock of another. The higher animals so stubbornly resist the intrusion into their own flesh of alien flesh, even of their own species, that only by the surgeon's utmost art can they be induced to accept a foreign organ to replace a diseased one of their own.
Even in their manner of destruction, living beings demonstrate their essential difference from the nonliving. Barring violent impacts and such crushing forces as might reduce rocks and crystals to rubble or powder and living flesh to formless pulp, organic and inorganic bodies are destroyed in radically different ways. Rocks weather on their exposed surfaces and slowly dwindle; crystals dissolve from the surface inward; drops of a liquid evaporate from the outside. But living things are so well enclosed in protective membranes or integuments that their destruction, when not caused by violence or high temperatures, usually results from changes in the interior rather than at the surface. The deadly poison or fatal parasite must insinuate its way into the body, either through one of the natural openings normally under the control of the organism or through a break in its integument, before it can begin its work of destruction. Or, if it escape death in other forms, the organism runs down and becomes quiescent from senescence, a process wholly internal.
The other distinctive qualities of living organisms are ancillary to their ceaseless effort to preserve separate identity. Most significant of these are their capacity to assimilate and incorporate intimately into themselves materials different from their own substance, and to grow from within rather than at the surfaceby intussusception rather than by apposition, as botanists say. Whereas crystals and other inorganic bodies that do not enclose themselves in insulating membranes may continue to grow by means of superficial deposits, this method of enlargement is not available to an insulated organic body.
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Living things tend to avoid contact with substances and processes that would harm them: a protozoan swims away from the diffusing chemical that would kill it; a man snatches his hand away from a hot stove. Inorganic bodies show no comparable tendency to avoid other bodies that would injure them. But the living organism does not always passively await actual contact with the deleterious substance; it displays a sensitivity to influences playing upon it, from sources near or remote, such as is rarely found in inorganic matter, and frequently it succeeds in escaping from dangerous situations. And when contact with the injurious foreign object is inevitable, it exhibits an ability to adapt itself, to escape destruction by changing shape and endless stratagems, for which one looks in vain in lifeless bodies.
But in spite of all its defenses and its wiliness in confronting unfavorable situations, the more highly differentiated organism must sooner or later succumb, if not by external agency, then by internal decay. Yet even mortality cannot defeat it. If it cannot maintain its separateness in its own body, it will transmit this capacity for preserving separateness to others like itselfnot only to one, but to several or many, to ensure the perpetuation of its kind against all contingencies. As though foreseeing its own eventual disintegration, it does