264 C. PFAFFMANN 



sodium need has been manipulated in man. Since salivary sodium levels 

 and salivary volume flow are sensitive to changes in serum Na and hydration 

 it is entirely possible that such threshold changes reflect changes in salivary 

 sodium and other electrolyte constituents. Thus, the electrophysiological 

 evidence just reviewed for chemical stability of receptor sensitivity can be 

 reconciled with the psychophysical studies on man. 



The question still remains on the relation between taste sensitivity and 

 preference behavior motivated by salt deficiency. Changes in sensitivity, 

 however induced, might increase the detectabihty of taste stimuli but there 

 is no necessary relation between enhanced sensitivity and preference. It 

 should be remembered that preferences in salt needy animals are enhanced 

 over the whole range of concentrations tested. Mere change in sensitivity 

 should increase the apparent strength of the higher but more aversive salt 

 stimuli. It is just these solutions that are taken with increased avidity. 



Another way to induce salt need is by dialysis with 5 per cent glucose 

 injected intraperitoneally in an amount equal to 10 per cent of the animal's 

 body weight. This draws NaCl into the body cavity as osmotic equilibrium 

 is established and, if this ascitic fluid is withdrawn after several hours by a 

 second intraperitoneal puncture, the animal is left in a highly depleted 

 sodium state. This results in increased drinking of sodium chloride solu- 

 tions and of water (Falk and Herman, 1961). In a single-bottle drinking 

 test, the dialyzed animal takes increasing amounts of salt solution, depend- 

 ing upon concentration, and shows an exaggerated preference-aversion 

 function (Richman and Pfaff*mann, 1962). 



Behavior in a two-bottle preference test is likewise altered. We have 

 studied this in a new version of the two-bottle preference test developed by 

 Dr. G. L. Fisher (1962) in our laboratory. The drinking tubes are pre- 

 sented alternately once a minute by a solenoid operated plunger so that 

 only one tube at a time is available to the animal. Tests are conducted for 

 20 min just after the animal has been fed and watered, at the same time 

 each day. An electronic record of drinking is obtained by a Grason- 

 Stadler drinkometer and cumulative recorder which advances the pen at 

 each lick. At the end of each, the recorder resets to zero as the one tube 

 retracts and the other is presented. 



Figure 5 shows the last session before and the first session after dialysis. 

 In the left record, the signal marker up means that tube no. 2, containing 

 water, is available ; signal marker down, that tube no. 1, containing salt, 

 is available. In the right figure, tube no. 1 contains H^O and no. 2, salt. 

 Before dialysis, a slight preference for saline is shown at the beginning of 

 the session, but the animal drinks little thereafter. After dialysis, much 

 greater drinking of salt ensues. Water is sampled but not consumed to any 

 degree, as shown by the square-topped drinking records. Not only is there 

 increased ingestion of salt, but there is a clear preference, after sampling. 



