PHYSIOLOGY OF CHEMORECEPTION 247 



Table 1. EEG and behavioral responses to pure chemicals and extracts 

 added to sea water.— Continued 



Range of 



concentrations EEG Behavioral 



Compound (molar) tested response response 



Miscellaneous extracts 



Holothurin (extract of 



Cuvier's gland of A ctinopyga) (N.A.) + 



Aplysia "ink" secretion (N.A.) 



Note: "+" indicates consistent EEG changes or positive behavioral responses. "— " in- 

 dicates lack of detected responses. (N.T.) designates not tested. (N.A.) designates 

 measurement not applicable. For further details consult text. 



sponses in these tests. The effect of the anesthetic in the nasal sacs made it 

 clear that gustatory receptors were not significantly influencing the re- 

 sponses being studied, and it was assumed that other chemoreceptors must 

 come into play later, when ingested material is very near or within the 

 mouth. 



Electrolytes— Two series of electrolytes were tested in what has be- 

 come a standard approach to analyzing the effectiveness of ions on chemo- 

 receptors. A series of different cations were tested, in combination with 

 one anion (Cl~); different anions were then tested in combination with 

 the same cation (K + ). Chemoreceptors of mammals and insects have been 

 shown to be particularly sensitive to cation effects, with the stimulating 

 effectiveness of various cations roughly parallel to their effective electro- 

 static field strengths (Hodgson 1974). However, the sharks, while showing 

 obvious awareness of the ionic stimuli, did not demonstrate differential 

 sensitivities that could be detected by these methods. Nor did they give 

 sustained behavioral responses to any of the electrolytes. 



The great sensitivity of the shark's olfactory system is illustrated strikingly 

 by the discrimination between artificial seawater (containing the 10 major 

 electrolytes of seawater) and the natural seawater of the test area. (This may 

 not be entirely on the basis of electrolytes, of course, since the artificial sea- 

 water would lack other compounds dissolved in natural seawater.) 



EEG responses of HgCl 2 and CuS0 4 were weak and of short duration, 

 probably a result of the toxic effects of these metal ions on the olfactory 

 epithelium (Hodgson 1965, Tester 1963). In behavioral tests in the large 

 enclosure, there were no sustained reactions, either positive or negative, to 

 HgCl 2 or CuS0 4 . This could be the result of the quick rinsing of the nasal 

 sacs during normal swimming, rather than the toxic effects observed in 

 tests in more confined quarters. 



