of protoplasm goes on the power of growth diminishes. I consider it probable that the growth and differentiation of protoplasm is the direct cause of the diminution of the growth power. The observations on growth bring out clearly to our minds the conception that the decline is by far the most rapid in the very early periods of embryonic development or, better expressed, that the rate of decline is at its maximum during the earliest periods. The older the individual becomes the less is the power of growth, but also the less rapid is the decline in that power. Thus we reach the paradoxical conception that the period of most rapid development is also the period of most rapid decline. This view, it seems to me, applies to all development, at least in the higher animals. As I have spoken on this subject more fully elsewhere, I will not pursue it longer now, but it seemed to me desirable to refer to it as an illustration of the far-reaching character and wide scope of embryological investigation, which inevitably allies itself with every other biological science.
It would be no difficult task to extend my discourse by multiplying illustrations of the beneficial influence of embryology upon other departments of medical science. It is one of the institutes of medicine—a part of the foundation of knowledge upon which medical practise is erected.
Embryology supplies facts which are directly valuable to the practitioner. It supplies explanations and interpretations of many anatomical structures and relations which would otherwise remain incomprehensible. It supplies the clues to many common and rare anomalies, and it supplies to pathology a series of fundamental conceptions, without which our actual present pathological knowledge could not have been upbuilt. These claims of embryology to recognition are very great, but nevertheless they do not include her greatest claim to a preeminent place among the medical sciences. That greatest claim is established in my opinion by the contributions of embryology to the solution of the problem of organic structure.
Structure is the only distinctive mark of living bodies, by which we know them to differ from inanimate objects. In the final discrimination between living and dead all other distinctions fail us or at best are utterly uncertain. In the higher forms we see differences of function always correlated with visible differences of structure. From such evidence, together with much other, we have established the hypothesis or theory—for at best it is only a theory—that all living functions are dependent upon organic structure. It is quaint, we may remark in passing, to read in recent essays by a learned German botanist the announcement of this theory, which the vast majority of biologists have long adopted, as a new foundation for biological philosophy, because he terms the ultimate unknown facts of structure 'Determinanten.' How often has science been impeded by the intru-
