But there are limits set to that struggle by man in the substitution, also within limits, of social progress for cosmic progress. In this _Ethical Evolution_ selfishness is so far checked as to permit groups of human beings to live together in amity, recognising certain common rights, which restrain the self-regarding impulses. For, in the words of Marcus Aurelius, "that which is not good for the swarm is not good for the bee" (Med., vi, 54). Huxley aptly likens this counter-process to the action of a gardener in dealing with a piece of waste ground. He stamps out the weeds, and plants fragrant flowers and useful fruits. But he must not relax his efforts, otherwise the weeds will return, and the untended plants will be choked and perish. So in conduct. For the common weal, in which the unit shares, thus blending the selfish and the unselfish motives, men check their natural impulses. The emotions and affections which they share with the lower social animals, only in higher degree, are co-operative, and largely help the development of family, tribal, and national life. But once we let these be weakened, and society becomes a bear-garden. Force being the dominant factor in life, the struggle for existence revives in all its primitive violence, and atavism asserts its power. Therefore, although he do the best that in him lies, man can only set limits to that struggle, for the ethical process is an integral part of the cosmic powers, "just as the 'governor' in a steam-engine is part of the mechanism of the engine." As with society, so with its units: there is no truce in the contest. Dr. Plimmer, an eminent bacteriologist, describes to the writer the action of a kind of yeast upon a species of Daphnia, or water-flea. Metschnikoff observed that these yeast-cells, which enter with the animal's food, penetrate the intestines, and get into the tissues. They are there seized upon by the leukocytes, which gather round the invaders in larger fashion, as if seemingly endowed with consciousness, so marvellous is the strategy. If they win, the Daphnia recovers; if they lose, it dies. "In a similar manner in ourselves certain leukocytes (phagocytes) accumulate at any point of invasion, and pick up the living bacteria," and in the success or failure of their attack lies the fate of man. Which things are fact as well as allegory; and time is on the side of the bacteria. For as our life is but a temporary arrest of the universal movement toward dissolution, so naught in our actions can arrest the destiny of our kind. Huxley thus puts it in the concluding sentences of his Preface--written in July, 1894, one year before his death--to the reissue of Evolution and Ethics: