88 NATIONAL TRENDS IN BIOLOGY 



long time in biological experimentation: (1) analysis of 

 the environment, and (2) the study of the physics and 

 chemistry of the substances of living things. To these we 

 have now added (3) the physical arrangements of both 

 gross and minute materials in the organisms. At the mo- 

 ment, therefore, we find many of our biological leaders 

 emphasizing not only the arrangement, but the varieties 

 of arrangement and the grouping of the arrangements in 

 the organism. 



H. S. Jennings has probably written most satisfactorily 

 on the factors confronting us in attempting explanations, 

 as well as on some of the more outstanding problems that 

 biologists are attempting to solve. We here follow his 

 reasoning though not his wording :^ 



As the properties of atoms depend upon the arrange- 

 ment of electrons, that of molecules upon the arrange- 

 ment of atoms, and that of crystals upon the arrangement 

 of molecules, a great extension of all these arrangements 

 is contained in the organism. Here the arrangements 

 have become quite complex and differentiated, forming 

 the visible as well as the invisible parts of the whole. As 

 one passes from one species to another, there is an almost 

 infinite variety of such arrangements. One might call 

 some of them "systems of structures," and consequently, 

 the way an organism responds to a stimulus or an experi- 

 ment of any kind will depend upon its system of these 

 diverse arrangements. 



From an acceptance of such facts, it follows that a 



