COMPARATIVE STUDIES ON THE SENSE OF TASTE 293 



example, in the case of calcium chloride, 17 apparently discriminated at 

 concentrations of 0.2 per cent or lower, 12 at 0.8 per cent, 14 at 1 .2 per cent, 

 and 13 had thresholds higher than 1.2 per cent. Thus the distribution of 

 thresholds was of a continuous type. There were no apparent sexual 

 differences in taste ability. No individual was completely taste " blind " 

 since all birds responded if the concentration reached a high enough level. 

 A chemical specificity was involved, since an individual that could taste 

 one chloride at a low concentration did not necessarily respond to other 

 chlorides at low concentrations. A bird that was indifferent to one chloride 

 often showed good taste sensitivity for another. 



In addition to these marked individual differences in threshold, there 

 were individual differences in preference behavior at low concentrations, 

 i.e., some mdividuals preferring a chloride and others rejecting it. How- 

 ever, most birds showed a pattern of increasing rejection with increasing 

 concentration. 



Williamson (Pers. Comm.) has carried the study of individual variation 

 to three generations. He screened 100 males for ferric chloride thresholds 

 and selected two birds, the ones with the lowest and highest thresholds, 

 and of 100 females selected 11 high and 9 low threshold birds. He then 

 performed a selective breeding program, breeding the high threshold male 

 with various high threshold females, and doing the same for low threshold 

 birds. The progeny were then tested for ferric chloride thresholds at 8 

 weeks, the same age as the parents had been tested, to avoid introducing 

 age as a variable. There was a statistically significant difference between 

 those with high and those with low threshold parents, indicating that ferric 

 chloride thresholds in the fowl have a genetic basis. 



In other related studies we used 12 breeds of chickens and found some 

 evidence of breed differences. Here again, it was one of degree rather than 

 absolute difference. Nachman (1959) has shown in rats that certain 

 individual differences in response to saccharin have a genetic basis. 



Since in the experiments with sugar chickens had failed to respond except 

 to xylose, work with series of sodium salts and various chlorides was under- 

 taken (Tables 1 and 2). Again as with the sugars, no physical or chemical 

 basis for preference (i.e., rejection) could be discerned. Toxicity was con- 

 sidered as a factor influencing preference since the chicks did reject some 

 toxic salts. However, since some salts destroyed all the chicks, toxicity 

 could not be consistently a variable. In the case of sodium tungstate at the 

 higher concentrations intake constituted a lethal quantity while at the 

 lower concentrations, although the salt was accepted indifferently, the 

 threshold for toxicity is not reached. 



One area in taste research that has been most interesting is the water 

 response observed in some animals (Zotterman, 1961). Special concern 

 was directed in our laboratory to the pH of the water used. The body 



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