I50 THEORETICAL BIOLOGY 



fold importance. Firstly, it enriches the world-as-sensed 

 with the things of space ; and secondly, it permits the animal, 

 as soon as the first spatial indications sound in the manner 

 characteristic for the schema, to form the whole schema, 

 and in this way to recognise the presence of, say, an enemy, 

 when the enemy is only partially visible. 



In the lower animals, the whole stimulus forming the 

 indication must get going, whereas, when there are schemata, 

 only the opening notes need sound for the whole schema to 

 act as indication. In this way, the schemata acquire a high 

 degree of independence in the steering mechanism. The 

 animal no longer flees before the direct stimulus of the enemy ; 

 it no longer is directly incited to seek its prey ; but it flees 

 from and seeks for the schemata of these. 



Up to this point the guiding apparatus in the brain can 

 now be traced with some certainty. All conclusions that go 

 beyond this point leave the firm basis of fact. For instance, 

 it is not yet possible to decide whether the law of the com- 

 plementary effect of colours is referable to a special arrange- 

 ment in the retina or to a special interlacing of the receptor 

 nerves in the brain, or whether it does not elude a mechanical 

 interpretation altogether. We have been able to establish 

 only this much — that we are dealing with a law belonging 

 to the subject alone, and completely independent of the 

 reciprocal action of the stimuli in space. 



In addition to the anatomical framework characterising the 

 guiding apparatus of the brain, we must also take account of 

 the brain's chemical framework. We can compare the effects 

 of the central nervous system on the muscles of the body 

 with a typewriter, in which the striking of each key releases 

 a certain letter. We get the same thing on the chemical side, 

 when we furnish the cells we want to affect with a specific 

 chemical substance that will combine with only one other 

 specific substance. 



