president's address. 5 



comluouplace. of physiology. And inasmuch as wu ourselves ate animals, 

 this conception gives us a certain insight into the reactions of planty 

 which -we should not otherwise possess. This is, I allow, a very dangerous 

 tendency, leading to anthropomorphism, one of the seven deadly sins of 

 science. Nevertheless, it is one that must be used unless the great mass 

 of knowledge accumulated by psychologists is to be forbidden ground to 

 the physiologist. 



Jennings ' has admirably expressed the point of view from which we 

 ought to deal with the behaviour of the simpler organisms. He points 

 out that we must study their movements in a strictly objective manner : 

 that the same point of view must be applied to man, and that any 

 resemblances between the two sets of phenomena are not only an allowable 

 but a necessary aid to research. 



What, then, are the essential characters of stimuli and of the reactions 

 which they call forth in living organisms ? Pfeffer has stated this in the 

 most objective way. An organism is a machine which can be set going 

 by touching a spring or trigger of some kind ; a machine in which energy 

 can be set free by some kind of releasing mechanism. Here we have 

 a model of at least some of the features of reaction to stimulation. 



The energy of the cause is generally out of all proportion to the 

 effect, i.e., a small stimulus produces a big reaction. The specific 

 character of the result depends on the structure of the machine rather 

 than on the character of the stimulus. The trigger of a gun may be 

 pulled in a variety of different ways without affecting the character of 

 tlie explosion. Just in the same way a plant may be made to curve by 

 altering its angle to the vertical, by lateral illumination, by chemical 

 agency, and so forth ; the curvature is of the same nature in all cases, 

 the release -action diffei-s. One of those chains of wooden bi'icks in which 

 each knocks over the next may be set in action by a touch, by throw- 

 ing a ball, by an erring dog, in short by anything that upsets the 

 equilibrium of brick No. 1 ; but the really important part of the game, 

 the way in which the wave of falling bricks passes like a prairie fire 

 round a group of Noah's Ark animals, or by a bridge over its own dead 

 body and returns to the starting-point, &c. — these are the result of the 

 magnificent structure of the thing as a whole, and the upset of brick 

 No. 1 seems a small thing in comparison. 



For myself I see no reason why the term stimulus should not be 

 used in relation to the action of mechanisms in general ; but by a 

 convention which it is well to respect, stimulation is confined to the 

 protoplasmic machinery of living organisms. 



The want of proportion between the stimulus and the reply, or, as it 

 has been expressed, the unexpectedness of the result of a given stimulus, 

 is a striking feature in the phenomena of reaction. That this should be 

 so need not surprise us. We can, as a rule, only know the stimulus and 



' The Beharior of t lie Loiver Organi$me, 1904, p, 124. 



