462 PHYSIOLOGICAL EEGULATIONS 



of an osmotic system. Output of water in both dogs and frogs is 

 generally believed to utilize hydrostatic pressures furnished by 

 cardiac muscle, and certainly other processes that at times oppose 

 osmotic pressures. The physical and chemical forces, processes, 

 and energies concerned in exchanges of water through kidneys 

 (aglomerular, pronephric, etc.) are known to be diverse among 

 species. In addition, all the species and living units that have no 

 kidneys may not be forgotten. To delay the study of water ex- 

 changes until the physicochemical nature of these processes is 

 known seems to me unwarranted ; it even seems doubtful that such 

 a millenial reward will ever arrive. 



Rates are what biologists observe; forces are what biologists 

 usually think they would like to measure. In practice, expendi- 

 tures of force are rarely directly measurable, and generally there 

 is no way of ascertaining the worth of what has been hypothesized 

 concerning them. Hence I emphasize that, instead of dynamic 

 equilibria and dynamic changes, I am studying kinetic equilibria 

 and exchanges. 



Wherever a believed force is operating at a known rate, the 

 ratio : force/rate, is a resistance. Much could be made of such re- 

 sistances with respect to the possible control of regulatory events. 

 By speculation, the living unit could be conceived as a large series 

 of resistances so arranged that each rate is adjusted by releasing 

 it to diverse extents. If it be supposed, conversely, that resistance 

 is constant in a variety of circumstances, then rates are propor- 

 tional to forces. In equilibrations, the stress, proportional to load, 

 is accompanied by a strain (force, rate) that accomplishes re- 

 covery. 



There is a belief that physiology can be approached only in pro- 

 portion as physics and chemistry are perfected and understood. 

 Physiology is even regarded as poorly developed physics and care- 

 less chemistry. A contrasted belief is that physiology is busy in- 

 quiring into relations, the relations being in combinations that 

 mostly do not occur in non-living systems. AVhile some methods, 

 apparatus, and symbols may be common to several sciences, biology 

 can also be independent of them, except to the extent of its recipro- 

 cal influence upon sciences of inorganic systems. Actually, of 

 course, most investigators bring facts and relations to light with- 

 out much respect to their beliefs about forces or vital processes, 

 and fortunately no formal division arises between orthodoxy and 

 unorthodoxy. 



