286 MORLEY R. KARE AND M. S. FICKEN 



strated to be erroneous using both electrophysiological and behavioral 

 techniques. The emphasis on man in the very early studies was probably 

 due to the ease of testing. The development of more objective testing 

 procedures was an important prerequisite to using the lower animals. 

 Perhaps the practical problem of maintaining large animals, or an exten- 

 sive array of animal species, has limited comparative studies. Another 

 factor delaying the appearance of comparative studies in taste was the 

 rather belated infusion of evolutionary principles into physiological re- 

 search. Comparative studies in anatomy had been popular for a long time 

 before Darwin, but this was not as true in physiology. This may have been 

 due to an apparent lack of applicability of physiological characters in taxo- 

 nomy, with which many of the zoologists of the time were concerned. 



One should consider function of taste in different animals, since it is on 

 this aspect that natural selection is acting. Unlike the other chemical 

 senses, which may have a variety of functions (i.e., mate selection, avoid- 

 ance of predators), the function of taste is more limited. It is reasonable to 

 ascribe to it a role in the regulation of ingestion of nutrients and possibly 

 the avoidance of toxic substances. It would be expected that the taste 

 system in a particular species would be adapted through the evolutionary 

 process to its metabolic and dietary requirements. 



The diet of animals in the wild is characteristic of the species. Although 

 chromatographic and other techniques may eventually make it possible to 

 work with the complex taste mixture of natural diets, sound experimental 

 design limits us to reagent grade chemicals. Only with such chemicals 

 can one confidently compare results or repeat experiments. 



A range of concentrations is used since species vary in degree of sensi- 

 tivity. In addition, a series of related chemicals are tested since this could 

 reveal a pattern of taste behavior which might be similar, yet not identical. 



Using the above criterion, Kare and Medway (1959) measured the 

 reaction of the fowl to a series of sugars in a two-choice situation where 

 distilled water was the alternative. The sugars were selected with a view 

 to introducing variables such as osmotic pressure, viscosity, nutritive 

 value, melting point, configuration, toxicity, solubility, rotation, sweetness, 

 and so forth. Some of the results are summarized in Fig. 1. Parenthetic- 

 ally, I would interject that the experiment failed to suggest any chemical or 

 physical basis to explain the fowl's preference reactions. 



The reaction of calves to common sugars is illustrated in Fig. 2. Even a 

 superficial examination leaves no doubt that the differences in reaction 

 between these two species are more than one of degree. Further, there is 

 no common pattern. This is amply illustrated with xylose which the fowl 

 finds markedly unacceptable and the calf obviously relishes. 



In Fig. 3 the response of rats to a variety of sugars was measured. The 

 range of concentrations tested was more extensive than with the fowl. It 



