THE POPULAR SCIENCE MONTHLY
structure and function of cells is to-day regarded as the basis of research in medicine as well as in biology. Yet all of it is traceable to the dissection of an ant beneath a crude microscope! Surely nothing would have seemed less likely to have had practical bearings.
Such studies have given also the basis for embryology, the analysis of the development of the individual. Perhaps the greatest marvel of nature is the growth and change of the individual, a process that is ever before us, yet considered by. few. From a microscopic egg cell that shows but few differences in its various parts, grows up the adult body with its manifold organs; hairs and muscles, bones and lungs, these are not present as such in the egg cell, yet they gradually arise out of it and in the order of their use. The problem is: is such development regulated by energies of the egg cell, or by the operation of new stimuli and energies as the development proceeds? The marvel is the astounding precision of the process in spite of its complexity. When you eat your morning egg glance at the yellow yolk ball and note at one point of its surface a small white disc; that is the egg cell proper, all the rest is simply food for it. Now try to think out how that little disc produces the complex fowl, and you will agree that the problem is a much harder one than the fluctuations of stocks in your morning paper. This problem has also a close bearing on medicine, as William Harvey pointed out some three centuries ago and more, for the development of the human body is as important to the physician as its anatomy, because the anatomy is but one view of the individual, while the development represents the whole. To understand our own bodies we must know how they are formed, and to understand disease it must be traced to its origin. The changes from the egg cell to the adult demonstrate that the longer a part develops, the more precise and fixed it becomes, so that finally each particular part comes to have one definite structure, position and use. Malignant growths, then, probably have their causes most frequently early in development, due to misplacement of cells, temporary arrest of growth, undue rapid multiplication of cells, and other abnormalities. But this is not the place to attempt to classify diseases on an embryological basis, such as has been done by Minot. We need note here only that medicine is beginning to tread in the path made by biology, in recognizing that human disease as well as human anatomy must rest on the foundation of development.
Then, to understand our own bodies we have to explain them in terms of the structure of other animals, and many of our parts would be meaningless to us but for a knowledge of comparative anatomy. Our cankered vermiform appendix is represented in some animals by a large and serviceable attachment of the digestive tract, which explains it as a degenerate organ and therefore necessarily variable. Deep