268 C. PFAFFMANN 



than the other arm which contained salt solution. Under these conditions, 

 the rat seemed motivated for water. A two-bottle preference test for the 

 rat with the same degree of deprivation, however, showed the usual 

 preference for salt over water. They believe that, in both cases, the mildly 

 thirsty animal desires water, not salt, but that in the drinking test he is 

 fooled by the taste of weak saline. Normally, the spontaneous discharge 

 of the taste receptor in the rat is reduced by water. Weak saline solutions 

 are less effective than water in reducing the resting activity, as shown in 

 Fig. 3. The smaller decrement to salt is said to be a "less good" water 

 signal and the rat must drink more saline to achieve an equivalent afferent 

 signal to water. 



As we shall see below, the preference for saline solutions as displayed 

 in the two-bottle test (24-hr ad lib.) may be regarded as a learned response 

 to the extent that the rat overcomes position habits in that situation and 

 learns where and how to find the salt which he prefers. When the 23-hr 

 thirsty animal is placed in a two-bottle situation, he drinks indiscriminately 

 (Treidman and Pfaffmann, 1961). If intake is followed minute by minute 

 in a 20-hr deprived rat, indiscriminate drinking of water and salt occurs at 

 first, but after 10 min of drinking, an increased intake of saline occurs 

 and the rat begins to display the preference for salt. At the end of a 20 to 

 30 min drinking test, the deprived animal will show a " salt preference " 

 in terms of final total fluid consumed, whereas there may be no salt 

 preference in the early minutes of drinking (Nachman, 1962b). In the 

 T-maze, on the other hand, the animal never drinks enough water (or 

 saline solution) to satisfy his thirst and, therefore, he remains thirsty 

 throughout the training and learns to go to water. Other evidence by 

 Mook (1962) tends to show that saUne solutions are less effective for 

 hydrating a deprived animal than plain water. Thus, the acquisition of a 

 response to the water side of the T-maze is to be expected. The Deutsch 

 and Jones results in the maze may depend primarily on thirst drive, whereas 

 the preference tests in the same animals are influenced by both thirst plus 

 the salt preference. The maze and preference test are two different 

 situations. 



Dr. Fisher's preference testing device with the alternate presentation of 

 water and salt was used to monitor the development of preference responses 

 to water and 0.1 m NaCl continuously over several 24-hr ad lib. sessions. 

 The positions of the salt and water were interchanged every 12 hr. In the 

 first 12 to 24 hr, all animals showed varying degrees of water and/or salt 

 intake but gradually, as the animals gained more experience with the 

 situation, they built up a stable and reliable preference for salt. In the 

 beginning, the animals seem to drink steadily at the first tube encountered ; 

 in some cases a position habit was evident. As time progressed, sampling 

 at both tubes became apparent and at a critical stage, usually late in the 



