No. 522] 



PHYSIOLOGICAL RESPONSE 



cury, kept them in liquid air at a temperature of — 190° 

 for three weeks and in liquid hydrogen ( — 250 ) for 

 three days. Is it possible to conceive of irritability ex- 

 isting under such conditions? Is it, indeed, possible to 

 conceive of life as latent ? I think not. Irritability must 

 be counted as completely lost during this time, and as 

 regained when the seeds germinated, as they did when 

 suitable conditions were furnished. To emphasize the 

 conditional nature of this quality, it may lie better to 

 describe protoplasm when irritable as in a state or con- 

 dition, instead of following the example of the physicist 

 in saying that it possesses the property of irritability, 

 of which it may be as surely dispossessed as steel may be 

 of its tenacity. 



Of recent years Bose has the merit of having insisted 

 upon the essential similarity of response in living and 

 in non-living matter. His "Plant Response" and " ( 'com- 

 parative Electro-physiology" are based upon this con- 

 ception; and though they contain much that can not be 

 approved, I am in complete accord with the thesis that 

 plants are intelligible only as mechanisms whose be- 

 havior, though more complicated than that of non-living 

 systems, is to be described by analogous laws. 



While recognizing the essential unit}- manifest in the 

 behavior of all matter, we must nevertheless discriminate 

 between physical and physiological response. It is not 

 possible, however, to use these terms as they have been 

 used, even by Bose, to designate, respectively, the re- 

 sponse of non-living and living matter, since many of the 

 responses of organisms are purely physical. Physical 

 response, as I conceive it, is marked by the fact that the 

 energy applied to the body is a full measure of the effect 

 produced. Thus, when the conductivity of a selenium 

 plate is altered by light, the molecular disturbance (if 

 we so explain it) is initiated by the radiant energy, and 

 the effect is precisely measured by the energy applied 

 from the outside. The selenium contributes nothing. It 

 is acted upon, and its condition is altered for the time 



