996. _Why do we taste?_
Because the tongue is endowed with _gustatory_ nerves, having the
function of _taste_ as their _special sense_, just as the _optic_, the
_auditory_, and the _olfactory_ nerves, have their special duties in
the eyes, ears, and nose.
997. _Why do some substances taste sweet, others sour, others salt,
&c.?_
It is believed that the impressions of taste arise from the various
_forms of the atoms of matter_ presented to the nerves of the tongue.
998. _Why do we taste substances most satisfactorily after they have
remained a little while in the mouth?_
Because the nerves of taste are most abundantly distributed to the
under surface of the tongue; and when solid substances have been in
the mouth a little while, they impregnate the saliva of the mouth with
their particles _and come in contact in a fluid solution with the
gustatory nerves_.
999. _Why if we put a nub of sugar to the tip of the tongue has it no
taste?_
Because the gustatory nerves are _not distributed to that part of the
tongue_.
[Verse: "Wine is a mocker, strong drink is raging; and whosoever is
deceived thereby is not wise."--PROVERBS XX.]
1000. _Why, when we draw the tongue in, do we recognise the sweetness
of the sugar?_
Because the dissolved particles of sugar are _brought in contact_ with
the nerves of taste.
1001. _Through what nerves are we made sensible of the contact of sugar
with the tip of the tongue?_
Through the nerves of _feeling_, which are abundantly distributed to
the tongue to guide it in its controul over the mastication of food.
1002. _Why do connoisseurs of wines close their mouths and distend
their chins for a few seconds, when tasting wines?_
Because they thereby bring the wine in contact with the under surface
of the tongue, _in which the gustatory nerves chiefly reside_.
1003. _Why do they also pass the fumes of the wines through their
nostrils?_
Because _flavour_, in its fullest sense, comprehends not only the
_taste_, but the _odour_ of a substance; and, therefore, persons of
experience attend to both requisites.
The various conditions of taste are defined to be:--
1. Where sensations of _touch_ are alone produced, as by glass, ice,
pebbles, &c.
2. Where, in addition to being _felt_ upon the tongue, the substance
excites sensation in the _olfactory nerves_, as by lead, tin, copper,
&c.
3. Where, besides being _felt_, there are peculiar sensations of
_taste_, expressive of the properties of bodies, as salt, sugar,
tartaric acid, &c.
4. Where, besides being _felt_ and _tasted_, there is an _odour_
characteristic of the substance, and essential to the full development
of its flavours, as in cloves, lemon-peel, caraway-seed, and aromatic
substances generally.
1004. _Why do we feel?_
Because there are distributed to various parts of the body fine nervous
filaments, which have for their special duty the transmission to the
brain of impressions made upon them _by contact_ with substances.
[Verse: "The works of the Lord are great, sought out of all them
that have pleasure therein."--PSALM CXI.]
1005. _In what parts of the body does the sense of touch more
especially reside?_
In the points of the fingers and in the tongue. By laying a piece of
paper upon a table, and upon the paper a piece of cloth, on the piece
of cloth a bit of silk, and on the bit of silk a piece of leather, so
that the edge of each would be exposed to the extent of half-an-inch,
it would be possible by the touch to tell when the finger passed
successively over the leather, silk, cloth, or paper, and arrived on
the table.
Those impressions of touch must have been communicated, with their
extremely nice distinctions, to the sensitive nerves that lie
underneath the skin, and must have been transmitted all the way through
the arm to the brain, although the touch itself was so light as
scarcely to be appreciable with regard to the force applied.
A hair lying on the tongue will be plainly perceptible to the touch
of the tongue; and the surface of a broken tooth will often cause the
tongue great annoyance, by the acute perception it imparts of the
roughness of its surface.
The toes are also highly sensitive, though their powers of touch are
seldom fully developed. Persons who have lost their arms, however,
have brought their feet to be almost as sensitive as fingers. Blind
persons increase, by constant exercise, their powers of touch to such a
degree that they are able to read freely by passing their fingers over
embossed printing; and they have been known to distinguish _colours_ by
differences in their grain, quite unappreciable by other persons.
1006. _Why is feeling impaired when the hands are cold?_
Because, as the blood flows slowly to the nerves, they are less capable
of that perception of touch which is their _special sense_. The skin
contracts upon the nervous filaments, and _impairs the contact_ between
them and the bodies which they touch.
1007. _Why do the fingers prick and sting when they again become warm?_
Because, as the warmth expands the cuticle, and the blood begins to
flow more freely through the vessels, _the nerves are made conscious
of the movements of the blood_, and continue to be so until the
circulation is equally restored to all the parts.
[Verse: "In the sweat of thy face shalt thou eat bread, till thou
return to the ground; for out of it thou wast taken: for dust thou art,
and unto dust shalt thou return."--GENESIS III.]
1008. _Why do persons whose legs and arms have been amputated fancy
they feel the toes or fingers of the amputated limb?_
Because the nervous trunk which formerly conveyed impressions from
those extremities remains in the part of the limb attached to the body.
_The mind has been accustomed to refer the impulses received through
that nervous trunk to the extremity where the sensations arose._
And now that the nerve has been cut, the painful sensation caused
thereby is referred to the extremity which the nerve supplied, and the
sufferers for a time appear to _continue to feel the part which they
have lost_.