WATER EXCHANGES OF DOG 41 



Three variables at a time can be represented in one diagram by 

 one set of accessory contours. With a three-dimensional figure, 

 four variables could be represented. For the present system of 

 variables that is unnecessary, since one of the above four variables 

 is a ratio between two others, and a two-dimensional figure is ade- 

 quate (fig. 20). On this one diagram may be represented the data 

 contained in all the foregoing figures. 



These four variables may be said to constitute the water-time 

 system for this particular species under the prescribed types of 

 load and the named conditions of environment. Such a system is 

 delimited by the describer. Correlations among these variables 

 characterize the responses to disturbances of water content with 

 respect to time and to accuracy of recoveries. 



§ 12. Stationary states of excess 



Thus far the responses have been described that follow a sudden 

 addition of water or end a privation of water. Other physiologi- 

 cal states have also been studied, in which the increment of water 

 in dogs in maintained steadily. Do they also help in understand- 

 ing equilibrations ? 



Positive increments (+ AW) are created by administering re- 

 peated doses of water by stomach at equal intervals of time (figs. 

 21 and 22). The process of loading the body with water is most 

 effective at first, for then nearly all the water put into the stomach 

 stays in the body. With the passage of time and the increase of 

 load, output becomes faster (figs. 23 and 24). Still, only at low 

 rates of water administration (M and N) does the rate of output 

 come to equal (at 1.5 hour) the rate of forced intake. Output also 

 becomes stationary over a period of time, and might remain so for 

 an indefinite period, if intake continued. When water administra- 

 tion ceases (at 2.5 hours) excretion is well under way, and no lag 

 occurs in the recovery ; in other words, the maintenance of a steady 

 output and the beginning of a recovery output are one process. 

 Throughout recovery the rate of water loss is closely proportional 

 to water load, or, the falling curves (as well as the rising curves) 

 of figures 21 and 22 are exponential with time. 



All this is shown in still another way by comparing simul- 

 taneous rates of intake and of output (fig. 25). The sequence of 

 exchanges is emphasized by this correlation. 



When the rates of water output are correlated with the loads 



