356 



SCIENCE 



I N. S. Vol. XXVIII. No. 716 



strength of the doctrine will insure its 

 final victory over the present anti-Darwin- 

 ian stream of criticism. From the Dar- 

 winian point of view it would be a re- 

 markable fact if the reactions of organ- 

 isms to natural stimuli were not adaptive. 

 That they should be so, as they undoubt- 

 edly are, is not surprising. But just now 

 I only call attention to the adaptive char- 

 acter of reactions from a descriptive point 

 of view. 



Hitherto I have implied the existence of 

 a general character in stimulation with- 

 out actually naming it; I mean the in- 

 directness of the result. This is the point 

 of view of Dutrochet, who in 1824 said 

 that the environment suggests but does 

 not directly cause the reaction. It is not 

 easy to make clear in a few words the con- 

 ception of indirectness. Pfeffer^ employs 

 the word induction, and holds that ex- 

 ternal stimuli act by producing internal 

 change, such changes being the link be- 

 tween stimulus and reaction. It may 

 seem, at first sight, that we do not gain 

 much by this supposition; but since these 

 changes may be more or less enduring, we 

 gain at least the conception of after effect 

 as a quality of stimulation. What are 

 known as spontaneous actions must be con- 

 sidered as due to internal changes of un- 

 known origin. 



It may be said that in speaking of the 

 "indirectness" of the response to stimuli 

 we are merely expressing in other words 

 the conception of release-action; that the 

 explosion of a machine is an indirect reply 

 to the touch on the trigger. This is doubt- 

 less true, but we possibly lose something 

 if we attempt to compress the whole prob- 

 lem into the truism that the organism be- 

 haves as it does because it has a certain 

 structure. The quality of indirectness is 

 far more characteristic of an organism 

 than of a machine, and to keep it in mind 

 '"Physiology," English edition, I., p. 11. 



is more illuminating than a slavish ad- 

 herence to the analogy of a machine. The 

 reaction of an organism depends on its 

 past history ; but, it may be answered, this 

 is also true of a machine the action of 

 which depends on how it was made, and in 

 a less degree on the treatment it has re- 

 ceived during use. But in living things 

 this last feature in behavior is far more 

 striking, and in the higher organisms past 

 experience is all-important in deciding 

 the response to stimulus. The organism 

 is a plastic machine profoundly affected 

 in structure by its own action, and the un- 

 known process intervening between stim- 

 ulus and reaction (on which the indirect- 

 ness of the response depends) must have 

 the fullest value allowed it as a character- 

 istic of living creatures. 



For the zoological side of biology a view 

 similar to that of Pfeffer has been clearly 

 stated by Jennings^ in his admirable 

 studies on the behavior of infusoria, roti- 

 fers, etc. He advances strong arguments 

 against the theories of Loeb and others, 

 according to which the stimulus acts 

 directly on the organs of movement; a 

 point of view which was formerly held by 

 botanists, but has since given place to the 

 conception of the stimulation acting on the 

 organism as a whole. Unfortunately for 

 botanists these movements are by the zo- 

 ologists called tropisms, and are thus liable 

 to be confused with the geotropism, helio- 

 tropism, etc., of plants: to these move- 

 ments, which are not considered by botan- 

 ists to be due to direct action of stimuli, 

 Loeb's assumptions do not seem to be ap- 

 plicable. 



Jennings's position is that we must take 

 into consideration what he calls "physio- 

 logical state, i. e., 'the varying internal 

 physiological conditions of the organism, 



' H. S. Jennings, " Contributions to the Study 

 of the Behavior of the Lower Orgahistns," Car- 

 negie Institution, 1904, p. 111. 



