uniformities and comparisons among components 385 



§ 138. Types of loading 



The means by which increments are produced in organisms 

 might merit an amount of study equal to that here put upon the 

 recoveries from increments. Indeed much effort in current physi- 

 ology goes into the search for methods and agents by which par- 

 ticular components may be experimentally disturbed. The means 

 (types) are in part peculiar to each class of organisms, and therein 

 define its properties. Increments of many, perhaps all, com- 

 ponents are to some extent avoided or resisted by organisms ; and 

 one study that might be made, though not attempted here, is to find 

 how few components suffer increment from each agent. 



An organism in balance is defined as one that maintains con- 

 stant, within measured limits, the contents of one or more specified 

 components. Persons who speak of positive and negative bal- 

 ances, would in my terminology speak of positive and negative 

 increments, or retentions and depletions. Similarly, those who 

 speak of ''levels" of intake would mean rates of intake or of turn- 

 over. "Levels" of concentration or of composition are, on the 

 other hand, usually contents of the component specified. 



Increments or loads arise incidentally in numbers of situations 

 in which the organism finds itself. Often loading is the organ- 

 ism's reaction to recognizable stimuli, often not. Descriptively 

 speaking, positive loads follow (a) forced gains at rates exceeding 

 the rates of loss, (b) inhibited losses at rates smaller than the rates 

 of gain, or (c) both. Negative loads follow the inverse conditions ; 

 but where no turnover is present only (a) is possible. For some 

 components only (b) is feasible. 



The load is maintained in a stationary state when forced gain is 

 equated with concurrent loss, or vice versa. Data of physiological 

 significance are obtained chiefly when the organism is free to man- 

 age at least one of the two exchanges ; ultimately it then exhibits the 

 load and rate characteristic of State III (fig. 180). When the ex- 

 perimenter decides the rates of both gain and loss, the organism 

 exhibits nothing but a changing load. When the experimenter 

 decides neither the intake nor the output, the organism enter State 

 IV and recovers (at characteristic rates). 



For some components the rate of some exchange in State IV is 

 not measurably different from the rate of its free exchange in State 

 III, at any one load. No method is apparent of predicting for 

 which components or under which conditions this holds true. There 



