Page:Popular Science Monthly Volume 7.djvu/178

166 the fragments to move one against the other, become covered with cartilage and encapsulated with fibrous and ligamentous tissues, so as to form the "false joint" of surgeons. Mucous membranes, when continuously exposed to the air, adapt themselves to their new situation by becoming covered with a layer of epidermis closely resembling skin. Of this we have a good illustration in long-standing cases of procidentia uteri, where the vaginal mucous membrane is often continuously exposed.

The vegetable world also furnishes numerous illustrations showing how plants adapt themselves, by modification of structure, to new conditions in which they have been placed. The geranium in our window, instead of growing in its naturally vertical direction, disposes its twigs and branches obliquely on one side, thereby adapting them, their leaves, blossoms, etc., the better to receive the rays of light that come in slanting through the window. Plants kept more or less in the dark, have a deficiency of color; they become bleached and white, but this lessened opacity of their skin, this increased transparency of tissue, enables them to make the most of what little sunshine is allotted them.

The sprouts of an onion or potato, when kept in a dark chamber, grow to an unusual length, and, although this elongation can accomplish no good when the bulb is packed in a barrel, or housed in a cellar, still it is evident that the plant is obeying the same laws of adaptive growth by which, when buried deeply in the earth, its sprouts increase in length until they reach the sunny surface of the soil.

Now, while these instances (and many others might be added) certainly furnish unequivocal evidence of a disposition on the part of organs and organisms to adapt themselves to new conditions in which they have been placed, and to altered functions they have been required to execute, yet it must be admitted they exhibit little or no proof that those other organic alterations, which we regard as fatal diseases, are imbued with the same conservative design. In fact, to meet the issue at once—to strangle the serpent before we take out his fangs—it is necessary to dispose of the objection that organic diseases, structural formations resulting from pathological development, produce physical pain, and lead to death; for that they do so is the common belief.

To meet this objection it is simply required to follow out the analogy, already alleged, between structures resulting from physiological development and those produced by development that is pathological. That the causes and objects of the two kinds of growths are the same, has been previously intimated. We proceed by calling attention to (what may surprise those who have not given the subject proper consideration) the great fatality attending physiological evolution:

Very young animals, and indeed young plants, are peculiarly liable to die before reaching maturity. This is especially the case in animals,