HerRICK, Organs of Smell and "I aste. 159 



is referred to the exposition and discussion ot the cerebral centers 

 for smell and taste given by Johnston and Herrick.- 



But despite these fundamental similarities, it still remains true 

 that the organs of smell and taste are topographically widely sep- 

 arated and structurally very different both peripherally and cen- 

 trally. Their central neural pathways and connections are in 

 fact as different as are those for hearing and vision, two senses 

 whose psychological and physical criteria are most clearly defined. 

 The anatomical relations of the gustatory system are known in 

 lower vertebrates and those of the olfactory system are well under- 

 stood and are tolerably uniform throughout the vertebrate series. 

 It is possible to determine by experiment to which one of the 

 peripheral sense organs an animal respondswhen given a chemical 

 stimulus. The anatomical criteria of smell and taste are therefore 

 clearly defined. 



As far as vertebrates are concerned, we may define taste in 

 accordance with the anatomical criterion as the reaction or sen- 

 sation arising from the appropriate chemical stimulation of the 

 organs known as taste buds (wherever found in the body), and 

 smell as the reaction or sensation arising from the appropriate 

 chemical stimulation of the termini of the olfactory nerve. (See 

 the Addendum, p. 165.) 



These definitions cannot be extended to the invertebrates unless 

 homologous organs can be discovered among them. It may well 

 be that there are no such organs in the invertebrates, a single 

 chemical sense alone serving their needs; or two or more chemical 

 senses may be present among the invertebrates which are wholly 

 unlike either of the vertebrate senses. 



In this discussion it will be observed that I take a somewhat 

 different standpoint from that of Nagel,^ who defined taste and 

 smell in terms of the state of physical aggregation of the stimulus. 

 Smell, he says, is the faculty of perceiving vaporous {dampfformtge) 

 substances and taste is the faculty of perceiving hquid substances. 

 It follows from this, he argues, that it is not proper to attribute to 

 aquatic animals a sense of smell in addition to a sense of taste, 

 but both functions fuse into a single one. 



^ J. B. Johnston: The nervous system of vertebrates. Philadelphia, 1906, chap. 10. 



C. JuDSON Herrick: The central gustatory paths in the brains of bony fishes. Journ. Comp. 

 Neurol, and Psych., vol. 15, 1905, pp. 450-454. 



' W. A. Nagel: Vergleichend physiologische und anatomische Untersuchungen iiber den Geruchs- 

 und Geschmackssinn und ihre Organe, mit einleitenden Betrachtungen aus der allgemeinen vergleich- 

 cnden Sinnesphysiologie. Bibliotheca Zoologica, Stuttgart, Helt 18. 1894. 



