Page:Popular Science Monthly Volume 7.djvu/185

Rh but even the color of the exterior presents the same unvarying uniformity of shade. The spots on the leopard and on the butterfly's wing, the speckles and stripes on the reptile, the scales of the fish, the plumage of the bird, and the fur of quadrupeds, are tinted so precisely alike in different individuals of the same species, age, etc., that we find it difficult to detect the slightest variation. Any appreciable deviation from the standard type must always be attributed to the action of some unusual cause disturbing the normal course of evolution, unnumbered instances of which appear among domesticated animals, where, in fact, uniformity is the exception and variety quite common.

Now, to go back to pathological evolution, we find the three qualities of graduality, latency, and uniformity of type, to belong also to it, i. e., when it has followed its undisturbed typical course. We observe, however, that graduality—slowness of organic change—is common only to so-called chronic pathological changes; in acute organic diseases (those that we have seen destroy life) the change of tissue is rapid; hence an organ undergoing pathological modification that becomes the seat of an acute process (of an acute inflammation) can no longer be said to have followed its designed typical course, and we can no longer anticipate the same attaining of the pathological evolution to its designed conservative, typical completion. The acute disease is accompanied with fever, hence with rapid wasting and reduced assimilation of food; it leaves the whole organism reduced in vital power, and there remain behind inflammatory products which require to be removed; the normal progress of the gradual pathological development has been arrested; the vitality of the part has been weakened; there is set up in it a tendency to degeneration or local death. Indeed, time would fail us to enumerate all the injurious consequences, immediate and remote, general and local, that are liable to follow even a single acute inflammatory attack. No wonder, when such attacks occur more than once, or are repeated over and over again, that the pathologically developing organ fails of reaching its designed conservative termination; it need never surprise us, under such circumstances, that the final result is degeneration and death instead of preservation and repair.

In the several instances (very simple ones) of admitted conservative modifications of structure previously mentioned, we observed that time was an important element. The enlargement of anastomosing arteries that took place after the main vessel had been tied, did so by slow degrees; so did the hypertrophy of the heart that followed more general arterial obstruction; so did the transformation of mucous membrane into skin when exposed to air; and so do all conservative modifications of structure when they have been allowed to pursue, undisturbed, their designed typical course.

Secondly, when typical pathological evolution follows its designed