488 



THE AMEBIC AX X. 1 TUBA Lis T 



[Vol. LII 



scribe a material system is in terms of the phase rule." 8 

 To apply these principles to the interaction of sys- 

 tems is the great practical problem. It requires, as pre- 

 viously mentioned, the analysis of the problem to such a 

 degree as to distinguish its different systems and homo- 

 geneous units, their degrees of freedom, their directions 

 of change, their cycles, their dynamic status and their 

 quantitative relations. Many of these action systems have 

 long been clearly recognized by plant and animal physi- 

 ologists and ecologists, as cells, tissues, organs and com- 

 munities, and many are recognized also in the physical 

 and chemical world, where much attention is given to dy- 

 namic relations. 



The processes of integration and dominance tend to 

 limit this diversity of systems. It is believed, however, 

 that to strive consciously for the application of those con- 

 ceptions with some idea of what they imply, will, how- 

 ever, greatly hasten progress. Further, by calling atten- 

 tion to these general ideas it may enable some investiga- 

 tors to become better prepared for handling them, be- 

 cause we may well recall Pasteur's remark that: "In the 

 fields of observation chance favors only the mind which 

 is prepared." It is hoped that by emphasizing these re- 

 lations others better qualified than I am will give atten- 

 tion to this subject, and supply numerous examples in the 

 various specialties; for it is by this method largely that 

 others can become interested and extend the applications. 



Up to this point the discussion has been mainly devoted 

 to the development of a dynamic conception of systems 

 and their methods of interaction. The migration of ani- 

 mals has long been recognized to include not only those 

 caused by the activities of the animal itself, but also by 

 the activity or agency of their environment; it is there- 



