Page:Popular Science Monthly Volume 71.djvu/122

death and final removal of the cells. The degenerative change always results in the death of the cell. In many cases the dead material is removed merely by being cast off, as is the case with the skin. All the scales which peal off from the outer surface of our body represent little scraps or clusters of cells which are entirely dead; and in the interior of the body, in the intestinal canal, and in the glands of the stomach, we find cells continually dying, dropping off from their place upon the walls, and being cast away. Or if we examine the saliva which comes from the mouth, we detect that that also is full of cells which have died and fallen off from their connection with the body and are thus removed. An even more important method of the removal of cells is by a chemical process in consequence of which the cells are dissolved and disappear before our eyes, very much as marble may disappear from sight under the corrosive action of an acid. Indeed, we know that all the parts of the body, so far as they are alive, produce within themselves a ferment which has a tendency to destroy the living substance itself. The production of these destructive agents is going on at all times, apparently, in all parts of the body, which are alive. A striking illustration of this is offered in the stomach. The digestive juice which is produced in the stomach is capable of attacking and destroying living substance, and any organic material suitable for food which is placed in the stomach will, as we know, be attacked by the gastric juices, dissolved to a certain extent by them, and so destroyed. Why then does the gastric juice not attack the stomach itself? This is but one phase of the problem why the body does not continually destroy itself. It has lately been ascertained by some ingenious physiological investigations that the body not only produces the destructive agents, but also antagonists thereto, anti-compounds which tend to prevent the activity of the destroying factors. The whole problem is one of great interest and importance which calls for very much further investigation before we can l)e said to have arrived at a clear understanding of it. But it helps us much in our conception of cytomorphosis to know that all portions of the body are endowed with this faculty of destroying themselves, for it enables us to understand how it is possible that after the degeneration of a cell it will be dissolved away. It is merely that the agents of solution which are ordinarily held at bay are no longer restrained, and they at once do their work. There is another, but comparatively rare, mode of cell-destruction. The cells break up into separate fragments, which are then dissolved by chemical means and disappear, by the method of histolysis above described, or else are devoured by the cells, to which reference was made in the first lecture, and which are known by the name of phagocytes, and to which Metchnikoff has attributed so great an importance. It is unquestionable that phagocytes do eat up fragments of cells and of tissues.