Excerpt from Science Progress in the Twentieth Century, Vol. 2: A Quarterly Journal of Scientific Thought; No. 5, July 1907 I may point out here that the first and second groups of tumours behave on transplantation as embryonic and adult tissues do, by exhibiting limited powers of proliferation, with the difference between cancer and embryonic tissue, that the former does not differentiate into an adult form. We are therefore able to place a positive value on the negative efforts which have been made to produce tumours by propagating normal tissues, and we are able to establish all gradations from the limited growth of normal tissues under experimental conditions, up to the remarkable phenomenon exhibited by the unlimited growth of the cells of some cancers under the same conditions. Thus experiment has bridged over the gulf between normal and cancerous tissue so far as their powers of growth are concerned. The limited growth of normal tissues, when transplanted, is independent of any extraneous organism. There is no need to assume such a dependence when cancerous tissues exhibit corresponding limitations; and if not, why should it be necessary to assume this intervention when the powers of growth pass insensibly through all gradations to those of unlimited amount? About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.