OTHER TYPES OF WATER INCREMENT 71 



cations of exchanges may be represented in a series of equilibration 

 diagrams (fig. 42). In them the shapes of the curves for intake 

 and for output have not changed, it is supposed, but only their 

 water contents at balance have shifted in diverse degrees. In 

 practice it is hardly possible to distinguish case BB from case CC, 

 since both show the same pattern of equilibration, and the displace- 

 ment of Wo in absolute or relative value might be quite small. 



Inhibition of intake and output together {e.g., by anesthesia or 

 pituitrin injections) may not change the analyzable content but 

 does temporarily modify exchanges. In such cases (§ 16, a, c) 

 there are two control or ''normal" rates of exchange, one for the 

 individual treated, the other for modal individuals or the same 

 individual untreated. 



Case DB', which exhibits both polyuria and polyposia, might be 

 judged to be in some state of diabetes insipidus, or of Eck fistula, 

 or other unusual character. Cases like DE', which have small 

 turnovers of water, exhibit oliguria plus oligoposia. 



If either the curve for water intake alone (BB' to AB') or the 

 curve for water output alone (BB' to BE') shifts, then the value of 

 Wo also changes. This contrasts with shifts of Wo which may 

 occur without any modification of the relative curves (BB' to EE') 

 for water exchanges. 



Changes in water content at balance (W©) undoubtedly are as 

 worthy of study as are those that excite equilibrations. The diffi- 

 culties in their accurate examination are greater, for Wo shifts only 

 in conjunction with contents of other components. Hence the cri- 

 teria of body weight and sensible water content are usually unsuit- 

 able, and two values of Wo can be compared only by {!) full 

 accounting for all water exchanges between the two, or (5) chemi- 

 cal analysis of paired individuals. Comparison of this kind re- 

 veals, however, the definite nature of the physiological state of the 

 dog with respect to water. 



§ 20. Summary 



Excesses and deficits of water may be produced in the dog in 

 various ways and under diverse conditions. Each type of load 

 requires distinct denomination, and accurate measurement of the 

 responses to it. Several states of narcosis, routes of water ad- 

 ministration, modifications of regime, and kinds of solutes added to 

 the water administered are here compared. Most rapid negative 

 loadings are obtained by intravenous infusion of solutions of 



