236 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 dis- 

 section 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 devel- 

 opment 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 mul- 

 tiplication 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 begin- 

 ning to tread in the path made by biology, in recogniziug 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 



