300 F. R. BELL 



remaining, tap water and sodium bicarbonate solution, was measured at 

 the same time each day and the amount consumed noted. In order to 

 prevent bias due to visual or behavioural cues the position of the test solu- 

 tion was reversed at the end of 24 hr. The amount of sodium bicarbonate 

 solution taken during a 48 hr period was expressed as a percentage of the 

 total fluid intake (i.e. test solution + water). These figures when plotted as 

 the ordinate show graphically the amount of liquid ingested daily as 

 sodium bicarbonate solution. 



The goats had been housed indoors for some months prior to the ex- 

 periments but they received an adequate diet including a balanced mineral 

 mixture which was always available to be taken ad lib. In two of the 

 animals sodium bicarbonate was introduced directly into the rumen com- 

 partment of the stomach by way of a previously prepared rumenal fistula. 

 Coincident with the beginning of this treatment there was a marked reversal 

 of the preference shown by the animals for the 1 per cent sodium bicarbon- 

 ate offered as an alternative choice to tap water. In the animal receiving a 

 daily supplement of 25 g the amount of sodium bicarbonate taken fell 

 below 25 per cent of the total fluid intake and even further, to less than 

 10 per cent, in the animal receiving 50 g/day sodium bicarbonate supple- 

 ment (Fig. 1). 



These results suggest that the parenteral introduction of the sodium 

 bicarbonate reduced the preference of the goats for sodium bicarbonate 

 over tap water. It is unlikely that the behavioural change is due to ali- 

 mentary osmotic effects since the total volume of liquid consumed remained 

 at a steady level. It would appear rather that by increasing the sodium 

 content of the plasma the sodium taste threshold had been lowered. The 

 failure to return towards a sodium bicarbonate preference on discontinua- 

 tion of the supplement suggests a repletion of sodium stores. There were, 

 however, two paradoxical features of this experiment, firstly plasma Na and 

 K levels showed little deviation from normal levels during the course of the 

 experiment, and secondly the animals did not react to maintain their 

 apparent sodium deficiency by taking sufficient quantities of the sodium 

 salts available in the mineral lick. 



A second experiment was set up designed to show the effect of smaller 

 amounts of sodium salts using a similar arrangement and the goats again 

 showed marked preference for 1 per cent sodium bicarbonate over tap- 

 water. 



After preference values had been established, a supplement of sodium 

 bicarbonate was administered daily for a limited period through a stomach 

 tube directly into the reticulo-rumen : by this means any permanent stress 

 due to the presence of the rumenal fistula was obviated but the buccal 

 gustatory receptors were not activated directly by the sodium bicarbonate 

 supplement. The experimental animals showed a change in preference 



