PHYSIOLOGICAL REGULATIONS 445 



is zero. To refer to the trougli as a locus of dynamic equilibrium 

 would add the inference that forces also have there a resultant of 

 zero, which is probable, but for them no measurement is usually 

 available. 



Maintenance and return to a mean position is illustrated, both 

 mechanically and physiologically, by tonus distribution in limb 

 muscles and tendons of man. The resting position of standing 

 erect means approximately equal lever tensions exist in antagonistic 

 muscles + gravity. Any inequality or movement is ultimately 

 recovered from by pull back to initial posture. This maintenance 

 represents a pattern of rates and forces in the body. It by no 

 means depends on gravitational forces alone any more than it 

 depends upon muscular forces alone. Here is an instance in which 

 actually more of the forces have been measured than of the rates 

 of transformation involved in their manifestation, and whatever 

 satisfaction lies in the study of forces rather than in the study of 

 rates of exchange is here available. A grand panorama of neuro- 

 muscular patterns is visible in that distribution of both forces and 

 rates, and dynamic and kinetic equilibrations might here be worked 

 out side by side. 



It has long been recognized that relations resembling equilibra- 

 tions occur in non-living systems. A general statement is the 

 theorem of LeChatelier ('84; '88, p. 48). Derived at first from 

 thermochemical studies, "if the solubility of a gas increases with 

 diminution of temperature, then its solution will take place with 

 the development of heat," the hypothesis now includes many other 

 phenomena. In current expression, the generalization is that "If 

 a change occurs in one of the factors determining a condition of 

 equilibrium, the equilibrium shifts in such a way as to tend to annul 

 the effect of the change" (Taylor, '24, p. 307). Change is speci- 

 fied, and rates of reaction are the usual measurements that illus- 

 trate it. While the phenomena studied are those of heterogeneous 

 systems, it is possibly misleading to extend the theorem itself to 

 living units that are exchanging with their environments. The 

 environment is in that case part of the system to be observed, and 

 metastable equilibria, reflexes, growth, and week-long recoveries 

 complicate the picture. Some day it may prove valuable to have 

 one theorem, or even one induction, for all those systems. 



There is regularly one value or range of values of each compo- 

 nent toward which the organism or species is indifferent, as, one 



