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Page:Popular Science Monthly Volume 70.djvu/498

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the brain is due in part to the shrinkage of the single microscopic constituents. There is another point of resemblance. We find that when one of the better parts of the body undergoes an atrophy, it becomes not only smaller, but its place is to a certain extent taken by the inferior tissues—especially by those which we call comprehensively the connective tissues, which might perhaps be best described to a general audience as that which is the stuffing of the body and fills out all the gaps between the organs proper. In consequence of performing this general function, they are very properly called connective tissues, since they connect all the different organs and systems of organs in the body together. Now in every body there is a continual fighting of the parts. They battle together, they struggle, each one to get ahead, but the nobler organ, generally speaking, holds its own. There are early produced from the brain the fine bundles of fibers which we call the nerves, which run to the nose, to the tongue and to the various parts of the body. When these appear all the parts of the body are very soft. Afterwards comes in the hard, and, we should think, sturdy bone, but never, under normal conditions, does the bone grow where the nerve is. The nerve, soft and pulpy as it seems, resists absolutely the encroachment of the bone, and though the bone may grow elsewhere, and will grow elsewhere the moment it gets a free opportunity, it can not beat the soft delicate nerve.[1] Similarly we find that the substance which forms the liver is pulpy, very delicate. Those of you who have seen fresh liver in the butcher's shop know what a flabby organ it is, and yet though it is surrounded by the elements of connective tissue, which with great zest and eagerness produce tough fibers, it never gives way to them. The connective tissue is held back by the soft liver and kept in place by it. The liver is, so to speak, a nobler organ than the connective tissue and holds sway ordinarily; but in old age, when the nobler organs lose something of their power, then the connective tissue gets its chance, grows forward and fills up the desired place, and acquires more and more a dominating position. We can see this alike in the brain of man and in the brain of the bee. That which is the nervous material proper, microscopic examination shows us to be diminished everywhere in the old bee and in the old man, and the tissue which supports it, which is of a coarser nature and can not perform any of the nobler functions, fills up all the space thus left, so that the actual composition of the brain is by this means changed. There is, you see, therefore, during the atrophy

  1. ↑ The nerve fibers of the olfactory membrane arise very early in the embryo and form numerous separate bundles. Later the bone arises between the bundles, for each of which a hole is left in the osseous tissue, so that the bone in the adult has a sieve-like structure, and hence is termed the cribriform plate. It offers a striking illustration of the inability of hard bone to disturb soft nerve fibers.