304 F. R. BELL 



levels for the sodium bicarbonate solution almost immediately but with 

 considerable variation between individuals (Fig. 2). In one animal a 5 g 

 daily (Fig. 2a) supplement was sufficient to change an almost 100 per cent 

 preference for sodium bicarbonate to a 100 per cent aversion whereas in 

 another animal a daily supplement of 60 g/day was needed to reduce the 

 animal's preference for sodium bicarbonate solution (Fig. 2b). In other 

 goats the response was intermediate so that relatively small amounts of 

 sodium bicarbonate altered the preference of the animals for sodium 

 bicarbonate with the result that less alkali was ingested. 



This demonstration that a preference for alkaline solution can be changed 

 to an aversion by administering a supplement of sodium bicarbonate is 

 striking. It is unlikely that the variation in taste is due to changes in 

 sensitivity of the peripheral receptors for Pfaffman and Bare (1950) have 

 shown in rats that salt deficiency following adrenalectomy does not alter 

 the thresholds of sensitivity. 



Apparently in the goats used in these experiments ingestion of sodium 

 salt is being controlled by some process which is dependent upon the 

 bodily supplies of sodium. It is possible that the controlling mechanism is 

 mediated through the adrenal cortex either directly by variation in blood 

 sodium levels or indirectly hormonally following the activation of meta- 

 bolic centres of the hypothalamus or in some other part of the brain. It 

 would appear that in the goats of these experiments the sense of taste is 

 being used to regulate sodium levels in the body and provides a good 

 example of the whole body self regulatory process postulated by Richter 

 (1943). 



The next experiments 1 want to discuss are concerned with variation in 

 preference thresholds for sodium in monovular twin calves. Monozygous 

 cattle twins were used because they have been shown to have very similar 

 threshold values for taste (Bell and Williams, 1959). Denton (1957) has 

 described a method of inducing sodium deficiency in sheep by exterioriza- 

 tion of the parotid duct when the continuous secretion of saliva causes a loss 

 of sodium from the body. Sheep made sodium deficient exhibit an avidity 

 for rock salt; the intake being 0.5-2.0 g/day in the normal state and 5-15 

 g/day when Na-depleted. The tendency towards sodium depletion in a 

 sheep with a fistulated parotid duct can be balanced by feeding a daily 

 supplement of 50 g NaHC03. 



When the parotid duct of a calf is exteriorized the effects are very 

 similar to those described for sheep. The salivary Na : K ratio is reversed 

 from 145 m-equiv/1. : 4.5 m-equiv/1. to 5.4 m-equiv/1.: 132m-equiv/l., 

 but it can readily be restored by feeding a supplement of NaCl or NaHCOg. 

 Salivary output from the exteriorized parotid duct decreases directly with 

 the degree of sodium depletion. At the same time the animal shows aphagia, 

 at first for concentrated food but later for all food including hay. The 



