has come very gradually. At first the student of medicine enlarged his field of study, from disease and its phenomena, until it included the structure and action of tissues and organs in health. Physiology and anatomy, of little importance in the old science of medicine, began to have recognized value. After this it was found that organs did not always become disordered because of assaults from within the body, but that they were affected by external influences.
It was found that the organs must not only preserve equilibrium within the body, but that there must also be equilibrium between the body and its externals. It was discovered that in every organ there were forces that built up and forces that pulled down, and that outside of it there were also conservative and destructive forces, and it became obvious that, unless these acted so as to preserve equilibrium, disease, and finally death, must ensue. Thus the art of healing and the science of medicine are now very far from being as simple as they were a century ago, and every year adds to their complexity. The physician of to-day must have full knowledge of man as man, of anatomy and physiology, as a necessary foundation upon which his further studies must rest.
Physiology especially has developed during the last fifty years, so that it has almost become a science by itself, but it still remains a part of the wider science of biology. Here again we see a difference between the studies of the ancient and modern physician. To-day, and still more in the near future, the physician must extend his studies beyond man, and the reason is plain. Man, with whom alone the physician formerly supposed himself concerned, is but an isolated being disconnected from the rest of nature. Nature tolerates no such isolation. No living being, even the simplest, exists, or can exist, independently of other beings. It affects them and is affected by them, and what is true of the simplest is yet more true of the more complex and most of all of man. Nature is one, and all her creatures are parts of the whole. For this reason man can not be fully known merely as man, he must also be known as a part of the animal kingdom. No one can well understand human anatomy or physiology who knows nothing of that of the lower animals. Comparative anatomy and physiology have thrown very much light upon many obscure problems to which the study of man gave rise. Therefore, I would most earnestly urge upon all medical men the study of biology. It may be replied that the courses of study are now crowded, but it is certain that the successful physician of the future must know something of nature as a whole. Already many of our most important theories as to disease—the structure of organs, cell-growth, cell-life, and many more—have come to medicine from biology. In an address before the International Medical Congress held in London in August, 1881, Professor Huxley remarks that "the search for the explanation of diseased states in modified cell-life, the discovery of the important part played by parasitic organisms in