284 CHEMICAL SENSES 



brevirostris), bonnet sharks (Sphyrna tibro), and nurse sharks (Gingly- 

 mostoma cirratum). Surface potentials of the telencephalon increased in 

 frequency and amplitude during chemical stimulation with various sub- 

 stances, such as the body fluids of crabs and glycine. Negative potentials of 

 various amplitudes, followed by lower potentials of opposite polarity, were 

 recorded 5 mm below the surface in the anterior halves of the lobes of the 

 forebrain, in response to extracts of tuna meat, dl-forms of glutamic acid, 

 glycine, cystine, serine, tuna blood, body fluids of lobsters and crabs, and 

 amine F, since identified as isoleucine methylester, an olfactory attractant 

 for lampreys, some teleosts, and sharks (Kleerekoper 1963 and unpublished 

 data). In later work, Hodgson et al. (1967), using similar techniques to 

 record EEG patterns in free-swimming sharks, restrained in a 60-cm-by- 

 420-cm tank, studied EEG characteristics as a function of olfactory 

 stimulation with a variety of substances and behavioral responses. Close 

 correlation between forebrain and medulla EEG patterns, and the behavior 

 of free-swimming sharks was established in response to various electrolytes, 

 amines, and amino acids. In nurse sharks, these responses were not affected 

 by removal of both barbels, but experimentally induced anosmia abolished 

 both the EEG and behavioral effects of chemical stimulation. 



THE ROLE OF OLFACTION IN FOOD PROCUREMENT 



It is of historical interest that some of the first scientific studies on olfaction 

 in fish included observations on food procurement in elasmobranchs (Scylio- 

 rhinus). Although Fabricius reported as early as 1753 on the response of 

 sharks to the scent of fouling meat, the first experimental investigation of 

 the sense of smell in elasmobranchs was done by Bateson (1890) in a study 

 on olfaction in fishes in general. By observing the behavior of normal and 

 anosmic animals he concluded that a number of fish species, including 

 Scyliorhinus caniculus, Raja cattis, Squatina squatina, and Torpedo, located 

 their food by olfaction. The normal fish, exposed to food odors in an experi- 

 mental tank, began to respond to the scent after it "had been diffused 

 through the water." They "swim vaguely about and appear to seek [the 

 food] by examining the whole area pervaded by the scent, having seemingly 

 no sense of direction whence it proceeds." The "process of search is equally 

 indirect and tentative by day and by night, whether food is exposed or 

 hidden in an opaque vessel, whether a piece of actual food is in the water or 

 the juice only, squeezed through a cloth and, lastly, whether the fish be 

 blind or not." Of particular interest is the observation that the response 

 never lasted longer than 15 min after introduction of the odor source into 

 the experimental tank. Evidence will be presented later that Ginglymostoma 

 continues to respond to food odor, presented in similar conditions, for long 

 periods. 



The choice of the species or even group of fishes by von Uexkull (1895) 

 was incidental to the purpose of his study, which was to decide whether 

 olfaction could function in the aquatic medium and to gather experimental 



