DESIGN FOR A BRAIN 17/4 



What of the case of Figure 16/6/1, when the parts of the environ- 

 ment are joined, and when what is done by, say, the reacting part 

 of A may affect, through the part B of the environment, what 

 happens at the second (B) essential variable ? In this case 

 co-ordination between the actions of the two reacting parts is 

 certainly necessary, for the desirable state of all essential variables 

 being kept within limits can be achieved only by each part's 

 actions being properly related to what the others are doing; for 

 all actions meet in the common environment. 



Given, then, that co-ordination between the reacting parts is 

 demanded, does this imply that the reacting parts must be in direct 

 communication ? It does not ; for communication between them is 

 already available (in the case considered) through the environment 



The anatomist may be excused for thinking that communication 

 between part and part in the brain can take place only through 

 some anatomically or histologically demonstrable tract or fibres. 

 The student of function will, however, be aware that channels are 

 also possible through the environment. An elementary example 

 occurs when the brain monitors the acts of the vocal cords by 

 a feedback that passes, partly at least, through the air before 

 reaching the brain. 



As the matter is of considerable importance in the general 

 theory of how organism and environment interact, and as it has 

 hitherto received little attention (though S. 5/13 touched on it), 

 let us consider an example that shows how functioning parts of 

 the brain may sometimes be co-ordinated by a channel of com- 

 munication that passes through the environment. 



Consider the player serving at tennis. His left arm makes a 

 movement that projects the ball into the air; a moment later, 

 his right arm makes a movement that, we will assume, strikes the 

 ball correctly into the opposite court. We will also assume that 

 the movements of the left arm are (for whatever reason) not 

 invariable but are subject to small random variations between 

 service and service. We assume that these variations are appreci- 

 able, so that unless the movements of the right arm are also varied, 

 and properly paired to those of the left, the ball is likely to go 

 out. Nevertheless we are assuming that the right arm's move- 

 ments are so paired that the ball arrives safely in the proper place 

 (' position of the ball's arrival ' is the essential variable, and its 

 normal limits are the bounds of the opposite court). 



220 



