COKEELATIVES OF WATER CONTENT 235 



By these criteria the modifications under diverse water loads of 

 the dog that at present seem suitable for routine use are: (a) total 

 dry residue of plasma, or any of its colligatives, (b) rate of water 

 exchange and (c) ''plasma" volume. It must be stipulated that 

 initial or control measurements be made on the same individual 

 when in water balance ; for most quantities vary among individuals 

 ■enough to make estimations of any but the most extreme loads of 

 water impossible in the living dog. 



One combination of modifications represents a water load of 

 specified type and amount. Moreover, by a sieving of the single 

 characters making up the combination, diverse types of load may 

 be distinguished, thus differentiating the water deficit studied by 

 Haden and Orr ( '23) or that studied by Gamble and Mclver ( '28) 

 from that studied by Herrin ( '35) or that shown in figure 122. 



Having aligned some of the variables correlated with body water 

 ^jontent in dogs, I can evaluate some of the statements that have 

 been made about water content. Frequent has been the use of the 

 terms dehydration, hydration, and the like. As these terms im- 

 plicitly referred to some one type or any group of types of water 

 load, whatever characterizations are suggested from time to time 

 may now be differentiated. 



(1) A view of water balance, proposed particularly by Gamble 

 ('29) is that the water content of the body depends on the total 

 solute present in the body. ''Volume is determined by the total 

 ■quantity of substances in solution. . . . The primary event on 

 which the loss of water depends is, namely, a loss of substance." 

 Gamble investigated dehydration by abstracting from dogs various 

 body fluids, particularly pancreatic juice, intestinal juice, and 

 gastric juice. That fact clarifies the meaning of his generaliza- 

 tion ; the generalization covers depletion of water content by taking 

 away body fluids, each of which contains solutes as well as water. 

 When on the contrary, solutes are not removed, body volume is not 

 proportional to the substances in solution, so that vapor pressure 

 or its colligatives are not constant (fig. 131). 



A further view, put forward by Magnus ( '00), is that "the blood 

 plasma may be completely sustained, over a considerable period of 

 progressive dehydration, by water and materials derived from 

 interstitial body fluids." (Gamble, '29, p. 912; also Underhill and 

 Fisk, '30, p. 349). Yet in another type of water deficit than theirs 

 -the blood plasma decreases in volume (fig. 114) and increases in 



