370 PHYSIOLOGICAL REGULATIONS 



and it is exponential, then the value of 1/At = /c is independent 

 of the fraction 1/a or the interval At used. 



Figure 180 describes, therefore, the relations to time in any dis- 

 turbance and recovery. A story concerning a particular compo- 

 nent may be planned by measuring those quantities that will fit it. 

 Conversely, all components may be compared by means of the 

 numbers found for each of the curves and parameters represented. 

 They seem to describe adjustments of any physiological compo- 

 nents. 



§ 134. Loads 



A load is defined as the deficit or excess of any measurable 

 component in a living unit, relative to its content in a control state. 

 A component is, in turn, any property of an organism that is sus- 

 ceptible of measurement. What are the several methods of 

 measuring loads? 



(a) Taking the organism or its part as it happens to be, the 

 investigator keeps a complete account of gains and losses while the 

 individual passes from state I to state III ; and later from state III 

 to state V. At the end he decides whether state V equals state I, 

 whether net gain or loss throughout state II equals net loss or gain 

 throughout state IV, and whether some of the component escaped 

 measurement by having been transformed. At whatever times 

 gains and losses are ascertained, the coincident loads and rates are 

 known. 



(b) By an appropriate kind of measurement that presumably 

 does not interfere with the physiological state, repeated determina- 

 tions of load are obtained. Examples of the kinds of measurement 

 that are available are: (!) Body weight or volume or length as an 

 indication either of total substance or of water content, depending 

 upon the conditions in which the measurement is applied. (2) 

 Determinations upon small tissue samples by a variety of physical 

 and chemical and serological procedures, with or without either 

 estimates of volumes of distribution or assumptions that volumes 

 of distribution remain constant. (5) Introduction in vivo of for- 

 eign indicators, either physical, chemical, or serological, usually 

 with subsequent sampling of tissue for analysis. 



The changes of load with time being known, the successive rates 

 of net exchange may be computed. Or, the changes of load with 

 time and the rate of total gain being known, the rate of total loss 



