SMELL, TASTE, AND CHEMICAL SENSE IN VERTEBRATES. 227 



stimulated by a bait on the sides of its body as well as at its mouth. Tests 

 carried out by me on specimens of Amiurus that had previously shown tin 

 reaction but in which the lateral accessory nerve had been cut, failed to elicit 

 this response. With the loss of the lateral accessory nerve there was always a 

 loss of response to ordinary bait, even though the fish remained reactive to acid, 

 alkaline, and salt solutions. That this failure to respond to bait was not due 

 imply to the shock of cutting nerves, is seen from the fact that when the lateral- 

 line nerves were cut, nerves larger than the lateral accessories, tin response to 

 bait was still easily elicitable. These observations show that t he lateral ace ,ry 

 with its taste buds as terminals adds considerably to the efficiency of the re- 

 sponses of Amiurus to such chemical materials as are contained in the food. 



I endeavored to discriminate between the n ponses due to the chemical 

 stimulation of the spinal nerves and to that of the taste buds by cutting the 

 lateral-line nerves and destroying the hind part of the spinal cord thus leaving the 

 posterior surface of the trunk and the tail innervated by the branches of the 

 lateral accessory nerves only. Fishes operated upon in this way, howevci lid 

 not respond to bait, nor to acid, alkaline, or salt solutions when applied to the 

 integument in the cord-less region. It is my opinion, however, that this absence 

 of response is due not so much to the ineffectiveness of the receptors of the 

 lateral accessory nerve as to the complete paralysis of the musculature of much 

 of the trunk and tail with which the fish habitually responds to such stimuli. 

 From the observations of Herrick (1903) and from my own, it seems probabl. 

 that the taste buds are in some way stimulated by sapid substances of significance 

 as food and as a result the fish turns the head towards the part stimulated. 

 According to my studies of the free-nerve terminals of the common chemical 

 sense, these receptors are stimulated by materials more in the nature of irritants 

 which lead the fish to avoid certain regions. 



The receptors in the olfactory organs of Amiurus, like those of other verte- 

 brates, are morphologically so distinct from the free-nerve terminals of the common 

 chemical sense, and the taste buds and fibers of the organs of taste, that it is 

 unnecessary to contrast them. Suffice it to say that olfactory cells, free-nerve 

 terminals, and taste buds seem to be the appropriate receptors for smell, the 

 common chemical sense, and taste respectively. 



5. A Physiological Comparison of the Chemical Senses in Vertebrates. 



In making a physiological comparison of the chemical senses in vertebrates, 

 only a limited range of observations are available. The early records of Nagel 

 (1894) on the stimulation of the skin of fishes by weak solutions of substances 

 that are normal stimuli for the organs of taste are so incompletely described that 

 !t is often difficult to draw comparisons, at least of a quantitative kind, with 

 the work of later investigators. My observations on the chemical sense of 

 Amphioxus (Parker, 19086) were scanty and my first report on the reactions of 

 niurm (Parker, 1908a), really a preliminary communication, was necessarily 



A 



