Page:Popular Science Monthly Volume 32.djvu/552



HEN one of the gall-flies (cynips) stings the tender shoot of a rose-bush, the poison which is deposited along with her eggs excites at that portion of the twig an excessive degree of nutrition, and the resulting swelling becomes the home of the young of the fly.

The rose-bush gall is composed of nothing more than ordinary vegetable tissues; but they are abnormally developed, and there is an accompanying modification in the growth of normal structures. For instance, the vegetable hairs at that point may increase in size until they resemble large thorns, and an involved leaflet may lose its identity and become a part of the tumor. The color-grains (chlorophyll), which should give to the bark a green color, may show various shades of red instead. The rose-gall is not very different from the morbid growths of animal tissues which appear as tumors of various kinds; and we know that some, and presume that many, of the latter, are due to the disturbance caused by the presence of humble parasites belonging to the vegetable world. These parasites, or microbes, as they are called, are so small that it is impossible at present to study the life-histories of some of the species. No one has satisfactorily described any specific cancer-producing microbe, but it was only yesterday that we became acquainted with the cousins which cause the development of the tumors of glanders, of tuberculosis, of carbuncle, and of "big-head" (actinomycosis)—so that, reasoning by analogy, it seems more than probable that all malignant growths belong to the infectious microbic diseases, and that by to-morrow we shall have the tiny causators in a position in which they can be examined.

The malignant tumors of warm-blooded vertebrate animals are divided into two great classes—the sarcomas and the cancers. These growths are like the galls of various plants, in that they are composed not of new tissues, but of abnormally arranged tissues of ordinary character. Structures in their vicinity lose caste and become merged into tissue of some one type, just as the leaflet gives up its position as a lung for the rose and helps to build a house for the young gall-flies.

We have in cancer a sort of anarchy of cells, as it were, in which the leaders, whose work, for instance, consisted in the construction of muscle, are routed from their high positions and forced to become common members of a low organization.

Like many popular names the term cancer is indefinite, but it is principally used to distinguish three or four forms of malignant growth from the sarcomas and from benign tumors. The benign tumors grow within limiting capsules; pushing other tissues out of the way as they increase in size, and showing no tendency to affect the