water exchanges of dog 49 



§ 14. Summary 



To find how the dog adjusts the content of water in its body, 

 unusual amounts of water are experimentally provided, and subse- 

 quent movements of water into and out of the body are observed. 

 It is found that excesses are removed chiefly through the kidneys, 

 at rates that are nearly proportional to the excesses ; while deficits 

 are made up with amazing promptness and exactitude by drinking. 

 Both recoveries are by modifications in rates of exchanges that 

 already are operating in turnover. 



Alternatively, excesses may be experimentally maintained by 

 continual addition of more water, and deficits by not allowing the 

 water that is drunk to be absorbed (esophageal fistula). Then the 

 time elapsing since the water load was imposed ceases to be an 

 important factor ; the rate of exchange is stationary. 



In all circumstances the relations between exchange and load 

 serve to describe the processes concerned in recovery from water 

 load. Such relations, represented in equilibration diagrams, indi- 

 cate the events by which the usual water content is restored, and 

 ordinarily is maintained. Partial representations are afforded 

 by various numerical means : velocity quotient, ratio of modifica- 

 tion, and economy quotient. These are several ways of comparing 

 the modifications of water exchanges that occur in the presence of 

 increments of water content. They concern only four sorts of 

 variables which for convenience are said to constitute the water- 

 time system of the dog. 



The relative effectivenesses of the separate paths of exchange 

 (urinary, evaporative) are rated according to the speeds with 

 which water flows through them at various increments. The net 

 effects in compensating for unusual water contents are the alge- 

 braic sums of these speeds. The fact that each rate of net water 

 exchange is proportional to water load appears to be a condensed 

 account of what the dog does to compensate for any disturbance 

 of its water content. 



