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possibly brutal and unintelligent, were normal beings with the activity and stamina necessary for future progress.

The following two diagrams, borrowed from these authors, represent clearly the differences between the initial and reduced condition of an organ or institution:

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In the diagrams the ascending lines represent the progressive evolution of an organ or institution; the descending lines represent the degenerative evolution. From the point a, representing the primitive condition progressive evolution passes towards o, an imaginary perfect condition of the organ. Along the upward line, however, the points a, b, c, d, etc., represent obstacles to further progress-that is to say, factors tending towards degeneration. From these points lines of degeneration pass towards z, and the condition at z, although representing that at a, is not identical

with a, and is not reached by a sliding backwards down the line o, a.

Thus, although the most recently acquired features may disappear first, degeneration is not an actual retracing of steps until the point of departure is reached. The degenerate condition is a new point, and really the term retrogressive evolution is misleading.

BOOK III

CAUSES OF DEGENERATIVE

EVOLUTION

PART I

ATROPHY OF ORGANS AND INSTITUTIONS

The factors of atrophy

THE causes which are active in producing degeneration are various, but they may all be referred to the limited nature of the means of subsistence, that is to say, of nourishment in the case of organisms, and of capital and labour in the case of institutions. This limitation produces a struggle between the individuals (societies or organisms) and between their component parts.

In the course of the perpetual struggle for existence among the different parts of an individual, the institutions or organs which have ceased to be functional tend to disappear, their nourishment being absorbed by the active parts.

1. Biology. In biology the struggle for existence among component parts appears clearly as a factor of degeneration in the case of accidental atrophy. This is to be seen, for instance, in the atrophy of

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the leaves of an etiolated plant1 or of the muscles of a limb which has been immobile for long, or in the case of muscles which have become inactive from disease of the central nervous system. The results are similar in cases of normal atrophy. In frogs, toads, and other Batrachia Anura,2 the disappearance of the tail before the adult state is reached is the result of a struggle amongst the cells. The active protoplasm of the muscular fibres develops specially, and gives rise to many cells, which enter the contractile material and separate its elements. Gradually all the contractile material is absorbed by these isolated cells.

Many plants, especially Sempervivum (see fig. 73, A, p. 236) possess a reduced stem with the leaves closely massed upon it. This reduction of the stem, which is nearly constant in the

1 When a cutting from a potato or a seed (fig. 75) is allowed to sprout in the dark, the young stems assume characters different from those of plants grown in light. The absence of chlorophyll produces important modifications of growth. In light the stem is short, and the leaves are large and expanded; in darkness the stem is very long, and the leaves are much reduced. This atrophy of the leaves is the result of the struggle for existence amongst the organs of the plant. Light increases the rate of transpiration, which is chiefly due to the presence of chlorophyll. As chlorophyll is most abundant in the leaves, the transpiratory current sets strongly towards them, carrying in it the nutritive materials for the formation of new cells. On the other hand, in etiolated plants, transpiration is slower, and the nutritive materials delayed in the stem give that the opportunity for specially active growth, which takes place at the expense of the leaves.

2 Metchnikoff, Annales Inst. Pasteur, January 1892.

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