CONTRIBUTIONS TO ZOOLOGICAL ANATOMY. 
587 
like manner, depends for its stimulus on the existence of sonorous 
undulations excited in, or transmitted to, the media in which its 
special nerve is situated. The existence and nature of the first of 
these stimuli, however, can only be proven by negative data, — 
the scholastic dogma of darkness proving the absence of light, — 
whilst the physical properties of the latter can be rendered more 
palpable, and can even be brought within the range of our cog- 
nizant senses. 
Of the three senses included in the second division, that of smell 
is the more special in its functions, requiring for its excitement 
to activity the “ local application” of external odoriferous particles 
possessing the physical properties of matter, and which properties 
can generally be reduced to a palpable and self-evident existence. 
No other function, however, can, by any reasoning, be assigned to 
the nose but that of smell, and the investigation of the minute 
structure of its component parts, in any class of animals possessing 
the sense, cannot adduce any facts tending to prove the contrary. 
This sense, therefore, may be looked on as possessing some of 
those properties which belong to the division of special senses, at 
the same time that it also exhibits phenomena (in so far as the 
physical nature of its stimulus is concerned) which require it to 
be classed with those of common sensation ; in fact, it is a link of 
union between those of special and those of common sensations. 
In man, and some others in the higher classes of animals, the 
tongue seems to serve the function of taste alone ; and on investi- 
gating the structure and conditions of its upper surface in these, 
this function can alone be assigned to it. 
In taking a review, however, of its uses in the various classes of 
the vertebratse, we cannot be justified in considering it as an organ 
of taste in all of them, although it was long the opinion of naturalists, 
that “ brute animals, especially those which feed upon herbage, and 
are not liable to be corrupted by example or necessity, distinguish 
tastes with wonderful accuracy. By the application of the tongue, 
they instantly perceive whether any plant is salutary or noxious ; 
and to enable them, amidst a thousand plants, to make this dis- 
crimination, their nervous papillae and their tongues are propor- 
tionally much larger than in man*.” This opinion, however, 
cannot be tenable on true zoological investigation ; and 1 shall 
prove in the following pages the very reverse, viz. that the 
smoother the surface of the tongue and the less developed are its 
appendages, the more acute is the sense of taste — thus verifying 
what was long ago observed by Shakspeare, that 
u The hand of little employment hath the daintier sense.” — Hamlet. 
* Smellie, Philos, of Natural Hist., vol. i, p. 166. 
