226 SMELL, TASTE, AND CHEMICAL SENSE IN VERTEBRATES. 



to the gustatory buds which, as Herrick (1903) has shown are distributed widely 

 over the trunk of Amiurus. The question to be decided is what part, if any, 

 each of these three systems of nerves plays in the reception of the stimuli recorded 



in the preceding section. # 



In selecting fishes for experimental work, individuals were first tested on the 

 tail and trunk to ascertain that they reacted normally to acid, alkali, and salt 

 solutions After this had been determined, the fishes were divided into four lots, 

 etherized and operated upon as follows: in the first lot, the olfactory crura were 

 cuf in the second, the lateral-line nerves; in the third the lateral accessory branch 

 of the seventh nerve ; and in the fourth both the lateral-line nerve and the lateral 

 accessory None of these operations were severe, for, in consequence of the 

 comparatively superficial course of the nerves involved, any of them could be 

 cut through slight incisions in the skin. The fishes were then allowed several 

 davs in which to recuperate and, after they had begun feeding regularly they 

 were tested with solutions of hydrochloric acid n/2, sodic hydrate n/40, and sodic 



chloride 2n. ... 



Fishes whose olfactory crura had been cut, showed the same sensitiveness on 



their trunks to acid, alkaline, and salt solutions that normal fishes did, thus 

 demonstrating that the reactions to these substances were not dependent upon 

 any accidental transfer of the stimulus forward to the nose. Fishes whose lateral- 

 line nerves had been cut, were also indistinguishable in their reactions to acid, alka- 

 line, and salt solutions, showing, as was to have been expected, that the lateral-line 

 nerves are not involved in these responses. Fishes whose lateral accessory nerve 

 had been cut, responded to the three stimuli in a way also mdistingmshable 

 from that of normal fishes. The same was true, as was to be expected, irom 

 fishes in which both the lateral-line nerves and the lateral a ccessones 7;~ 

 It, therefore, appears that the reactions in the trunk and tail regions of Amurus 

 to acid, alkaline, and salt solutions are not dependent upon the olf actory ^organs, 

 the lateral-line nerves, or the lateral accessory nerves. Hence they mus t oe u 

 to the stimulation of the only remaining nervous mechanism, the ordinary p 

 nerves whose free terminations in the epidermis must be regarded as the recep ■ 

 organs for this sense. This conclusion, stated by me in a P re ™ mar ^ * d 

 (Parker, 1908a), has been abundantly confirmed by Sheldon (1909) in n* 

 of the dogfish, niuch of whose integument is innervated by spinal ner ^ 

 As the nerve terminals in the exposed and partly exposed mucous surtac ^^ rf 

 higher vertebrates, where the common chemical sense occurs, ? r °\ clu de 



the spinal nerves in the skin of fishes, free-nerve terminations, it is tan >i ^^ 

 that this form of nerve ending is the characteristic receptive organ tor in rf 



chemical sense. Nerve fibers with such endings may be associated w 

 the general cutaneous nerves of the head or trunk in vertebrates. rminat } 0I1 s 

 If the common chemical sense has for its receptors free-nerve e ^^ 

 in the skin of Amiurus, what then is the significance of the taste . g 



over the outer surface of this fish? Herrick (1903) has shown that a 



