history of their own throughout the embryonic period and do not contribute in any way to the formation of any of the organs of the body. Since then Mr. B. M. Allen has discovered that the history of the germ-cells in the turtle is strikingly similar, and Dr. Woods is now engaged in tracing out the history in birds. Every one present will, of course, immediately recognize the great importance of a discovery which tends to show that there is a permanent distinction between the reproductive cells and the somatic cells which belong to the body and do not serve for reproduction.
Concerning cytomorphosis I need not add anything to what has been said concerning its general value in pathological study, but I should like to refer briefly to the good results which we may anticipate from direct application of the notions supplied by embryologists to the investigations which are yet to be made upon what we may call the morphological diseases, in distinction to those which are of parasitic origin. Morphological diseases arise through intrinsic causes, abnormal conditions due to the body itself and its reactions. Parasitic diseases have extrinsic causes. The dramatic—I might almost say melodramatic—growth of bacteriology and the kindred sciences has caused us to give most of our attention to diseases of the infectious type caused by some vegetable or animal parasite. This tendency is to be so far regretted that it has rendered investigation one-sided and lured it away from the class of diseases which may be attributed to pathological cytomorphosis. In regard to these the fundamental problem is identical for the pathologist and embryologist. It is the question of what and how the change in the structure of the single cell may be. Here is a central problem about which a vast number of lesser problems revolve like satellites. In the solution of this and of allied problems our greatest hopes for the future progress of medicine seem to lie. If we can find out what are the conditions which cause a cell to change its structure and advance in its cytomorphosis, we may hope that that discovery will include the explanation of why certain cells develop abnormally and become, as we commonly say, pathological, and we are to have precise knowledge of the cytomorphic causes we may dare, even now, to hope that we shall learn to regulate them, and that some, at least, of the diseases which are now beyond our reach will come under our control. It was not long ago that the idea of conquering diseases like malaria, yellow-fever, diphtheria and tuberculosis seemed a mere dream, a beautiful dream, yet control of them is now a reality, and is becoming almost daily more assured, complete and beneficent. So too in regard to the strictly morphological diseases, knowledge may bring mastery; and even sclerosis, that disease from which we are all assumed to be suffering in varying degrees, may, ere long, find itself subject to man.
Of the services which embryology has rendered to medical science
