204 PHYSIOLOGICAL KEGULATIONS 



may be classed as follows. Each is measured by clock in relation 

 to physiological events. 



(A) Initial interval after increment is imposed, or after 

 recovery begins. It may be the first one hour (Atj), or the interval 

 for half the load to be dissipated (Atn). 



(B) Uniform interval, often in a stationary state (Atg). 



(C) Interval containing maximal rate of exchange (Ati,). 



(D) Interval including complete recovery (AtR). 



(E) Instantaneous intervals along the time axis (AtM). 

 Types of increment of water content (AW) may be grouped. 



Each is measured on one species by one method, such as body 

 weight, liquid volume, ratio water/dry weight. 



(A) Net deficits, (a) By water privation, (b) By hypertonic 

 solute, (c) By previous exosmosis. Etc. 



(B) Net excesses. Each may follow single or repeated admin- 

 istrations of water (a) By mouth or stomach, (b) By injection : by 

 vein, under skin, into peritoneal cavity, (c) By previous en- 

 dosmosis. Etc. 



(C) Net random changes, (a) Control conditions, (b) Un- 

 usual temperatures, (c) Unusual physical exercise. Etc. 



(D) Gross exchanges, ± SW per unit At. Each may or may 

 not be corrected for control rates. According to paths as follows : 

 (a) Gain: alimentary, metabolic, cutaneous, (b) Loss: urinary, 

 vacuolar, fecal, evaporative, (c) Both: osmotic. 



The bases for these classifications are, as in all classifications, 

 those of dimensions and of utility in thought. While AW and At 

 may be varied in infinite types and intervals, only two algebraic 

 signs (deficit, excess) prevail in AW and only one sign in At. The 

 varieties (types) of AW and of At are not infinite in number but 

 correspond to procedures and conditions for observations and 

 measurements. In other words, types of load and classes of time 

 intervals are treated as discontinuous variables, leaving the four 

 continuous variables to be graded according to their numerical 

 values. Each category could, of course, be subdivided further or 

 in a different fashion. Thus, with respect to urinary loss, one 

 nephron could be studied ; with respect to metabolic gain, the water 

 formed from one precursor or in one organ could be measured. 

 In general, while the four sorts of variables are distinguished by 

 their physical dimensions, the subdivisions depend on physical and 



