either novel or familiar conditions. A river (organism) 

 shows regulation in migrating from its original channel to 

 one of greater stability, and in overcoming obstacles, such as 

 log jams or landslides, which serve as the cause of their own 

 remedy. 



In the above examples correction is the result of the 

 excess of process, or deviation from stability. The correction 

 and the condition which needs correction may, however, both 

 be the results of the same cause, having no causal effect on 

 each other. For instance, in crayfish oxygen starvation is 

 corrected by the very activity which causes it, namely, walk- 

 ing. The gills are placed so as to be moved by the legs, 

 for which reason walking causes both depletion and repair 

 of the oxygen content of the blood. Another example is 

 found in the protective color changes in the coat of northern 

 mammals. These changes are possibly not the result of the 

 color environment (the seasonal variation of which is a devia- 

 tion toward instability), but rather the result of some ac- 

 companying condition such as food or temperature plus certain 

 internal factors. That is, the brown fur does not become 

 white because of the whiteness of the snow. The cause to 

 which is due in part the occurrence of the snow, namely, a 

 decrease in temperature, is largely responsible for the adapt- 

 ive change in the color of the fur. Again, for example, the 

 sunshine which on a summer day would otherwise overheat 

 a man, is in part the cause of the breezes which assist in 

 keeping him cool. The cause, that is, which produces the 

 deviation from the optimum brings about also a condition 

 which helps to restore the optimum. 



We may then occasionally find this relation between 

 the deviation from stability and its means of correction. The 

 mutual cause of these two processes may indeed be in- 

 definitely remote. This phase of regulation is not recog- 

 nized in the above definition, so we may add: Negative regu- 

 lation also occurs when a process in the manifold which is 

 the cause of a deviation from stability results independently 

 in its correction. 



FIVE] 



