PHYSIOLOGY OF CHEMORECEPTION 249 



EEG records showed slight responses during tests with glycerol and the 

 fatty acids, but there were no consistent behavioral changes with these 

 compounds as stimuli. The emulsions were nonstimulating, with one curious 

 exception. A lemon shark happened to approach the tygon tube through 

 which linoleic acid emulsion was being introduced; a violent shaking of the 

 shark's head was observed, and the animal quickly swerved and swam away 

 from the stimulus source and olfactory corridor. This incident is mentioned 

 because isolated episodes of violent aversive reactions do occur from time 

 to time, and it is tempting to interpret them as indicating the repellent 

 capacities of the stimuli. However, they cannot be repeated consistently. 

 Rather than repellent actions, most such events observed in these experi- 

 ments were more likely the result of startle responses or transient irritation 

 effects from the introduction of high concentrations of the emulsions into 

 the nasal arcs. The absence of responses to the fish oil extracts supports 

 the view that these oils are not major chemical cues in prey -seeking behavior. 



Purified blood fractions— Although attraction of sharks to fresh 

 blood in the water has been observed many times, the results of controlled 

 tests with stored blood, usually outdated supplies from hospital blood banks, 

 have been ambiguous. Sometimes such tests elicit oriented approaches by the 

 experimental sharks, sometimes not. Moreover, the obvious next step of test- 

 ing carefully refined components of whole blood, to determine the attrac- 

 tive chemicals more specifically, was handicapped by the unavailability of 

 most suitable fractions for testing, and by the high costs of the few that were 

 available. The latter possibility has recently become more feasible through 

 the availability of commercial supplies of purified blood components from 

 nearly a dozen mammalian species. 



Taking advantage of the purified blood fractions available, we chose a 

 test series to include major fractions of human and bovine blood compo- 

 nents, with the ultimate choices depending on relative costs and availability 

 at the time of testing. Because the behavioral thresholds were significantly 

 lower than EEG responses, the blood fractions have thus far been tested only 

 for behavioral responses of free-swimming sharks. The fractions listed in 

 Table 1 were introduced in the test enclosure as concentrates freshly ob- 

 tained from commercial suppliers. 



At least brief awareness responses were obtained from both nurse and 

 lemon sharks contacting the olfactory corridors formed by all the blood 

 fractions. The human and bovine hemoglobins (2X crystallized) elicited 

 clear orientation and approach reactions, with significant increases in the 

 swimming speeds of responding lemon sharks. Less stimulating, but still 

 eliciting positive orientation and approaches, were the human and bovine 

 albumen (crystallized) fractions. Globulin (beta globulin, Cohen fraction III) 

 did not elicit sustained orientation responses. 



These results are encouraging in that they indicate the varied effectiveness 

 of different purified blood fractions. However, they are not yet susceptible 

 to more detailed interpretation. It seems likely that breakdown products in 

 seawater, perhaps amino acids, are the essential stimuli involved. It is also 



