Chapter II 

 WATER EXCHANGES OF DOG 



§ 6. Of the several approaches to the study of regulations, the 

 compensations manifested when an animal has unusual amounts of 

 water in the body call for intensive consideration. The object is 

 to find how the water content is restored after it is disturbed from 

 complacency, after water is forcibly added to or subtracted from 

 what is usually there. 



Among the relations of water content, it seems to me desirable 

 to study features available in all organisms and their parts and 

 aggregates. The amount of water present in the living unit, and 

 the rate at which it is gained or is lost are, in that respect, suitable 

 quantities. Each has distinct dimensions. The amount of water 

 present is measured either in physical units, or else in physiologi- 

 cal units that are obtained by comparing the state of the organism 

 having much or little water witl^ its control state as it exists before 

 or after or omitting the treatment or condition. The physical unit 

 is the liter or the gram ; the physiological unit is a relative measure, 

 such as a relative increment of weight. 



The initial investigation of water exchanges by living units is 

 limited, while dealing with one individual animal (g) in one set of 

 observations (f) and by one path of exchange (p), to variables of 

 four dimensional sorts: Water increment (AW), water exchange 

 (R, or SW/At), time elapsed (t) after establishment of a new water 

 content, and velocity quotient (k or 1/At). Rate of exchange, R, 

 is thus a ratio of a quantity of component to an interval of time ; 

 and velocity quotient, obtained by dividing a rate of exchange by a 

 content, is a reciprocal of an interval of time. Intensive treatment 

 of these four quantities (in chapters II to IX) concerns the one 

 bodily component water. 



With regard to the component water, excesses are first imposed 

 in the form of water by stomach and deficits in the form of priva- 

 tion of water. Two types of water excess or deficit are succes- 

 sively studied : the temporary state following a single administra- 

 tion or deprivation of water (§ 7 to § 10) and the stationary state 

 in which excess or deficit is maintained approximately constant for 

 some period of time ('§12 and §13). Total exchanges are mea- 



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