3/15 THE ORGANISM AS MACHINE 



to something very different from what it was originally. The 

 results of these primary operations will thus distinguish, quite 

 objectively, the essential variables from the others. 



3/15. The essential variables are not uniform in the closeness or 

 urgency of their relations to lethality. There are such variables 

 as the amount of oxygen in the blood, and the structural integrity 

 of the medulla oblongata, whose passage beyond the normal limits 

 is followed by death almost at once. There are others, such as 

 the integrity of a leg-bone, and the amount of infection in the 

 peritoneal cavity, whose passage beyond the limit must be regarded 

 as serious though not necessarily fatal. Then there are variables, 

 such as those of severe pressure or heat at some place on the skin, 

 whose passage beyond normal limits is not immediately dangerous, 

 but is so often correlated with some approaching threat that is 

 serious that the organism avoids such situations (which we call 

 ' painful ') as if they were potentially lethal. All that we require 

 is the ability to arrange the animal's variables in an approximate 

 order of importance. Inexactness of the order is not serious, for 

 nowhere will we use a particular order as a basis for particular 

 deductions. 



We can now define ' survival ' objectively and in terms of a 

 field : it occurs when a line of behaviour takes no essential variable 

 outside given limits. 



43 



