6 rHESIDEN'T's ADDRESS. 



the response, wliile the intermediate processes of the mechanism are 

 hidden in the secret life of protoplasm. We might, however, have 

 guessed that big changes would result from small stimuli, since it is clear 

 that the success of an organism in the world must depend partly at least 

 on its being highly sensitive to changes in its surroundings. This is the 

 adaptive side of the fundamental fact that living protoplasm is a highly 

 unstable body. Here I may say one word about the adaptation as 

 treated in the Origin of Sj)ecies. It is the present fashion to minimise 

 or deny altogether the importance of natural selection. I do not propose 

 to enter into this subject ; 1 am convinced that the inherent strength of 

 the doctrine will insure its final victory over the present anti-Darwinian 

 stream of criticism. From the Darwinian point of view it would be a 

 remarkable fact if the reactions of organisms to natural stimuli were 

 not adaptive. That they should be so, as they undoubtedly are, is not 

 surprising. But just now I only call attention to the adaptive character 

 of reactions from a descriptive point of view. 



Hitherto I have implied the existence of a general character in 

 stimulation without actually naming it ; I mean the indirectness 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 conception of indirectness. 

 Pfeffer ^ employs the word inchictioji, and holds that external stimuli act 

 by producing internal change, such changes being the link between 

 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 considered 

 as due to internal changes of unknown origin. 



It may be said tha,t 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 doubtless true, but we possibly lose 

 something if we attempt to gompress the whole problem into the truism 

 that the organism behaves 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 is more illuminating than a slavish 

 adherence to the analogy of a machine. The reaction of an organism 

 depends on its past history ; but, it maybe 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 received during use. But in living things 

 this last feature in behaviour 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 struc- 

 ture by its own action, and the unknown process intervening between 



' Physwlogy, Engl, edit., i. p. 11, 



