488 H. S. Jennings. 



course does not exclude the possibility of the direct action of 

 agents on the body substance. The operation of intense physical 

 and chemical agents may injure or destroy the substance of which 

 the organism is composed, and with it the organism, in spite of 

 any reaction the organism can give. Second, the organism can 

 perform only those movements which its structure permits. 

 Often none of these movements can relieve the existing inter- 

 ference with the physiological processes. Then the organism 

 can only try them, without regulatory results, and die. Examples 

 of this are seen in the behavior of Paramoecium, or of Planaria 

 w^hen placed in heated water. Both animals perform practically 

 all the reactions of which they are capable, before they succumb. 

 Third, certain responses may become fixed, in the way sketched 

 above, because under usual conditions they relieve the organism. 

 Now if the conditions change, the organism can respond at first 

 only by this fixed reaction, and if this does not relieve, the animal 

 may be* destroyed before a new regulatory reaction can be 

 developed. This condition of affairs is widespread among 

 animals. 



All together, the regulatory character of behavior as found 

 in many animals seems perhaps intelligible in a perfectly natural, 

 directly causal way, on the basis of the principles brought out 

 above. We may summarize these principles as (i) the selection 

 by varied movements of conditions not interfering with the physio- 

 logical processes of the organism; (2) the fixation of the move- 

 ments by which the selected conditions were reached, by the law of 

 the readier resolution of physiological states after repetition. 

 Neither of these principles seem to contain anything specifically 

 vitalistic, or opposed in principle to what we find in the inorganic 

 world. 



Is it possible that regulation is based on similar principles in 

 other fields than behavior? Bodily movement is only one of the 

 many kinds of activity that may vary, and variations of any of the 

 organic activities may impede or assist the physiological processes 

 of the organism. Is it possible that interference with the physio- 

 logical processes may induce changes in other activities — in 

 chemical processes, in growth, and the like — and that one of 

 these activities is selected, as in behavior, through the fact that 

 it relieves the interference that caused the changes.'' 



There is some evidence for this possibility. Let us look for 



