468 PHYSIOLOGICAL EEGULATIONS 



component depend upon the contents and rates of exchange of other 

 components. 



(4) Theory of conservation. Rates of turnover are usually 

 near the minimum compatible with indefinitely continued function. 



(5) Theory of intermittencies. Long-time regulations, gover- 

 nor-like in action, influence intermittent exchanges (such as alimen- 

 tation and sexual expression). The average rate over a long- 

 period of time is thus uniform, though composed of discrete periods 

 of quick activity. 



(6) Theory of relative modifications. In one individual or spe- 

 cies, the exchanges of each component are modified so that they 

 remain compatible with one another over wide ranges of possible 

 loads. (Thus, water loss by vaporization does not overshoot the 

 requirements of coincident heat loss.) 



(7) Theory of velocities. For one component, diverse species 

 tend to have modifications of rates that bear the same proportions 

 to the load. Or, velocity quotients are rather similar in various 

 animals. 



(8) Theory of time scales. Single components and groups of 

 components tend among many species to unload in relatively simi- 

 lar times. Comparative physiology may be built upon the quanti- 

 tative diversities of time scales and their correlatives. 



(9) Theory of exponential recoveries. A majority of velocity 

 quotients (1/At) are roughly constant over wide ranges of loads, 

 times, rates, and past treatments. This is especially noteworthy 

 where diverse physical, chemical, and anatomical elements and 

 processes are known or believed to be concerned in the exchanges. 



(10) Theory of accommodation. Rates of exchanges are some- 

 times greater in response to great accelerations and decelerations 

 of load than they are at stationary loads of the same magnitude. 



(11) Theory of physiological magnitudes. Loads and ex- 

 changes may be studied and compared without reference to physical 

 and chemical categories in which constituent processes may be 

 classified. Similar loads, rates, and correlations constitute like 

 physiological attributes, within the limits described by their dimen- 

 sions. 



(12) Theory of physiological purpose. ^'All the vital mecha- 

 nisms, varied as they are, have only one object, that of preserving 

 constant the conditions of life in the internal environment" (Ber- 

 nard, 1878, p. 121). 



