THE VARIATION IN TASTE THRESHOLDS OF RUMINANTS 307 



it finds the saline solution and immediately begin to drink. This type of 

 self-selection behaviour provides further support for Richter's view and 

 indicates that the sense of taste can play an important part in the " en- 

 vironmental homeostasis " of the ruminant herbivores. Recent work in 

 sheep and cattle suggests that the Na/K ratio of saliva is a variable quantity 

 which may be reflecting fluctuation in the sodium status of the animal 

 (Sellers and Dobson, 1960 ; Bailey and Balch, 1961). The rise in the 

 potassium content of the saliva results from increased secretion of adrenal 

 corticosteroids due to sodium depletion (McDonald and Reich, 1959). 

 Although the adrenal gland is the main source of the controlling mechanism 

 of electrolyte control in sodium depleted sheep it is possible that other 

 areas, perhaps some part of the central nervous system may also be con- 

 cerned (Coghlan, Denton, Coding and Wright, 1960). 



It becomes apparent, therefore, that in ruminants there is a close inter- 

 relationship between taste, metabolism and nutrition. At present the 

 experimental data are sparse but the availabiHty of a good experimental 

 preparation augurs well for future investigations. 



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