270 C. PFAFFMANN 



" dilute water ". If the animal wants water, it is hard to see why he stops 

 drinking water in order to take saline, the less good or more " dilute 

 water ". Other evidence by Young and Falk (1956) and Falk (1961) also 

 points to the fact that the salt preference can reflect itself even in loco- 

 motor responses, i.e. preferential running to saline. All these results are 

 incompatible with the Deutsch and Jones formulation. 



Mook's (1962) ingenious " electronic esophagus " makes it possible for 

 the experimenter to deliver the same or diff'erent solutions through an 

 entubed gastric fistula while the animal drinks. The fluid which the 

 animal drinks escapes through the esophageal fistula but, since a drinko- 

 meter monitors the rate of licking, appropriate volumes of test fluid may 

 be introduced into the stomach by a solenoid pump system. If the stomach 

 receives the same solution that the animal drinks, then the normal 

 preference-aversion functions are obtained for NaCl, sucrose, and glucose. 

 Instead, if pure water is intubed, then the response to these three solutions 

 is markedly changed : NaCl no longer yields a preference-aversion 

 function ; sucrose and glucose yield functions with concentration which 

 resembles the chorda tympani discharge function for sugar as described 

 by Hagstrom and Pfaflfmann (1959). Mook concludes that in normal 

 animals salt drinking is largely a function of hydration and hence not 

 determined by taste. The sugar responses are clearly more taste determined. 

 Mook, however, points out that his data refer to a single-bottle intake 

 situation in a somewhat thirsty animal. This would tend to maximize the 

 hydration, post-ingestion effects. Desensitization by dealTerenting the 

 tongue or ablating the primary gustatory relay of the thalamus disrupts 

 the usual preference-aversion behavior in the otherwise normal animal. 



The animal can drink both solutions but has no sensory cue. Both 

 preference to salt and sugar as well as the aversion to quinine were markedly 

 reduced by lesions in the medial tip of the ventro-basal tip of the rat's thala- 

 mus (Abies and Benjamin, 1960 ; Oakley and Pfaflfmann, 1962). Figures 9 

 and 10 show the great reduction in preferences to both salt and sugar we 

 observed. The areas ablated correspond to the regions from which 

 electrical activity may be recorded (Pfaflfmann, Erickson, Frommer, and 

 Halpern, 1961 ; Emmers, Benjamin and Blomquist, 1962; Benjamin, 1962). 

 If post-ingestional factors alone were responsible for the behavior, we 

 should expect ageusia or hypogeusia to have much less effect on intake than 

 they actually have. 



There is still another class of behavioral methods, the operant procedures 

 developed by B. F. Skinner (1938) that can be used to assess the role of 

 taste stimuli in controlling behavior. Many types of taste solution may be 

 used as positive reinforcers for a bar pressing habit. The particular utility 

 of these methods for taste studies is that the experimenters can maximize 

 taste and minimize post-ingestional effects by using appropriate schedules 



