CONFORMITY WITH PLAN 331 



In this way he has succeeded in explaining a number of 

 kinds of animal movement as " tropisms " (i.e. a movement 

 directed from without). Heliotropism, phototropism, geo- 

 tropism, rheotropism, etc., have become useful shibboleths 

 to include a great number of similar movements in very 

 different animal groups. 



But Loeb's doctrine has not gained any general recognition, 

 for it leaves out of account essential parts of the animal 

 organisation. A living creature, even if we try to regard 

 it as a mere machine, does not consist merely of an effector 

 portion, as our machines do ; but also of a receptor portion, 

 which first converts all the influences of the external world 

 into an indication which then deals with the steering-gear. 

 And it is not permissible to put on one side this important 

 part of the life organisation, as Loeb has done. Even when 

 externally directed forces are present, these must transform 

 themselves within the animal into an indication, which then, 

 in accordance with these external stimuli, prescribes the 

 animal's own direction. 



If we wish to compare machines with animals, we must 

 first, then, construct them to correspond with the animal 

 body. It is not enough to assign to them elastic forces 

 of their own, which can be released by selected external 

 forces and so perform actions. This is found also in the 

 effector portion of the animal organism. The part that 

 makes the selection must be 'fitted up before the steering- 

 apparatus, if the external stimulus is to act as the direction- 

 giving indication. Even in this case, the resemblance would 

 continue to be purely external, because every organism consists 

 of cells, which are all of them active, both as receptors and 

 as effectors. 



And in addition to all this, the super-mechanical capacities 

 of the organism are not taken into account. 



Apart from these shortcomings, Loeb's doctrine remains 



