160 SMELL, TASTE, ALLIED SENSES 



bitter sense than of the sense of taste. Just as the sense 

 of feehng in the skin has been shown to consist of at 

 least four senses, touch, pain, heat, and cold, so taste must 

 be regarded as composed of at least four senses. That 

 these act together and in everyday experience produce a 

 unified effect upon us is no more reason for classing them 

 as one sense than in the case of the integumentary senses. 

 The sense of taste must, therefore, be regarded as a ge- 

 neric term under which at least four true senses are gath- 

 ered : sour, saline, bitter, and sweet (Oehrwall, 1891, 1901) . 



Although the sense of taste thus loses a certain amount 

 of its reality, the senses classed under it probably possess 

 a kiud of genetic unity that is not without significance. 

 It is very probable that these four senses represent four 

 lines of differentiation that have evolved from a single 

 ancestral sense. The remarkable uniformity of their 

 structure is suggestive of this view. If the four senses 

 under discussion have had some such origin as that just 

 indicated, the term sense of taste might well apply to 

 that primitive state, perhaps represented m some of the 

 lower vertebrates today, from which the four gustatory 

 senses of man have been derived. 



17. Comparative. The comparative physiology of 

 taste in vertebrates is almost an untouched field. The 

 distribution of taste-buds in the vertebrate classes indi- 

 cates the presence of this sense in the mouth regions in 

 forms as low as the amphibians. In fishes Herrick ( 1903) 

 lists over thirty-five species in which taste-buds are knoAvn 

 to occur on the outer surface of the animal as well as 

 in the mouth. The catfish Amiurus is remarkable in this 

 respect in that its whole outer surface is provided with 

 these organs which are most abundantly present on the 



