18 PHYSIOLOGICAL REGULATIONS 



sured, followed by separation into paths: Urinary water, evapora- 

 tive water, fecal water, water formed in metabolism (oxidative), 

 and water ingested as such (ingestive). One species (dog) is 

 initially studied, and the whole body is a unit, it being of no concern 

 for the present where within the body the water is. 



Confusion may be avoided by further defining a few quantities 

 to be used, particularly in connection with the graphical represen- 

 tation of data. Any departure of water content (W) from the 

 control content (Wo) is designated as water load, ± AW. Quanti- 

 tatively the unit of load is defined as an amount of water, weight, 

 or other equivalent equal to one-hundredth of the control live 

 weight of the body (Bo) or AW = 100 (W — Wo) /Bo. Each type of 

 modification of the water content has a slightly different definition 

 within the general class ; each may be measured by a partially dif- 

 ferent procedure, or under different conditions ; and some will be 

 in milliliters per gram, others in grams per gram. 



Similarly, interval of time (to — ti) is designated as At. Usually 

 the unit of time is the hour, but the hour selected may be various : 

 the initial hour, the hour of maximal load, an hour's duration of an 

 instantaneous rate, hour computed from half -hours, quarter-hours, 

 minutes, or days, and many others. It seems to me that clarifica- 

 tion is obtained by multiplying distinctions just so far as actual or 

 probable differences exist in the phenomena described. 



While the dogs are endowed with the diverse increments of 

 water content, their rates of total water exchanges (SW/At) are 

 measured, during the passage of time (t) after the increment is 

 established. Rates are expressed in per cent of body weight per 

 hour, or aW/At = 100(Wo — Wi)/BoAt. 



Thus I have elected an experimental situation and a set of vari- 

 ables to be measured. Their definition constitutes the design of 

 the initial investigation. 



§ 7. Sudden excesses of water 



Water contents are conveniently modified by administering 

 known quantities of water to dogs that are initially in control state. 

 How long do excesses remain? Knowledge that water was the only 

 liquid or solid given the dog saves the great trouble of evaluating 

 the water contents of dogs sacrificed and analyzed at diverse inter- 

 vals in each test. The quantities of water present and the ex- 

 changes are both measured by body weight, since the amounts of 



