sion of a pedantry which mistakes the invention of a new term for the introduction of a new idea!
To find out what structure really is is the goal of all biological science. When we discover this secret, we may hope to discover also how structure functions and why it exists. The problem of structure—of organization—is double; there is first the question, what are the essential qualities of the structure of living matter as such, and there is, second, the question of the variations and specializations, which structure may undergo. With both of these questions embryology is confronted and both of them it is seeking to answer. The first is the riddle of life. Embryologists are bravely attacking it and have, I believe, already made a little real progress towards its solution. To them it presents itself as a series of queries concerning the germ-cells and the fertilized ovum. Searching analyses of the details with the highest powers of the microscope and the most refined technique coupled with experiments have indeed increased our knowledge of the organization of the germ cells. America, thanks to the brilliant work of E. B. Wilson and E. G. Conklin, and of their associates and followers, occupies a leading position in this difficult exploration. The importance of knowledge of the fundament of organic structure can hardly be exaggerated, and when it is obtained it will, I may prophecy, have profound far-reaching and enduring effects upon all medical science.
Even more intimately is embryology occupied with the second part of the problem of structure, namely, the question of differentiation, i. e., of the gradual production of the varied organization of the adult with almost innumerable unlike parts. To-day the central problem of biology is that of differentiation, and the main purpose of cotemporary embryological research is to attack that problem. The problem is three-fold, for we must learn what differentiation is, how it is produced, and why it is produced. Embryology might almost be termed the science of organic differentiation. Now all that you do, as practising physicians, is to deal with differentiated organs and tissues. You deal with a function, normal or diseased, which is rendered possible by the differentiation of cells. You deal with pathological states, every one of which has its special differentiation. Every phenomenon which you encounter in your professional work is conditioned by the differentiation of the organic living substance. To regulate that differentiation, to set it right when it has gone wrong, is the brightest vision of future human power which I can conceive, and I can not but think of embryology, which strives unceasingly to discover the laws of differentiation, as that Institute of Medicine which is to be the foundation of a greater practical medical progress than any yet achieved. The physician's knowledge is the mother of mercy.
