The sun., 1893-06-04

l
there is q painful sensation referred to the OK
tremities Of the nerve. The exposed pulp Of a
| diseased tooth when irritated by hot or cold
fluids gives rise to pain. but not to the sensa-
| tions OF Temperatures Recent observations
| show that thero arc minute areas on the akin
| I'm which sensations OF heat and cold may DO
moro acutely felt than In adjoining aroas.
| Some OF these areas are m ore sensitive to cold.
| and hence arc called cold spots. whio others.
moro sensitive to heat. have received the
| name OF hot spots. They seem TO he or to
| contain end organs. arranged in points sub
| servient to a thermometric sense. 1t ia true
| that no terminal organ for this sense has yet
| been found. but inasmuch Us electrical or
| mechanical stimulation OF tho hot or cold spots
| calls forth the correspon ling sensation, the
| inference Is reasonable that such an organ
| exists II is also considered highly probable
| that there nro nerve fllaments specially do
| voted to conveying to the nerve centres what
| may be term ed thermal MS DISTINGUISHED from
| tactic i'm presslons. and thero may DO parts OF
tho brain whose specific function 1t Is to trans
late such Impressions Into sensations OF
temperature. To be distinguished likewise
from the tactile sense properly SO called. Is tho
muscular sense. which depends on sensory
nerves originating in the muscles and carry
Ing i'm pres ssions from these to tho nerve CEN
| tres. Finally. when active movements are
made by which a limb 10 placed In a certain
fatiguing position. we have contributing
to tho mental representation OF this
position not only tactic and muscular i'm
pressions. but also sonso OF the ei-
fort neces ary to cause tho muscles to perform
the movement This sense OF effort has been
called a sense OF innervation. and is distinct
both from the muscular sense and from tho
sense OF touch.
H.
Tho sense OF taste Is located chiefly In tho
tongue, but Gustatory sensations may also DO
referred to tho soft palate. and even to the
region OF the fauces. The mucous surface OF
the tongue is covered with minute promi-
nences or papillG, OF which there are three
kinds Most abundant are tho hliform papiilp.
small cylindrical bodies about twelfth OF an
inch long. Interspersed with these are the
fungitorm papille SO called because each looks
somewhat like q mushroom. consisting OF n
narrow stem supporting q Gattened top. They
may often be detected by their bright rcd
color Toward the root OF tho tongue We md
the third kind OF papillr. tho circumvallnte.
eight to flfteon in number. arranged In the
form OF V. with tho apex directed back
ward. In many OF the fungiform aud In all
tho circumvallate papillD arc minute oval
bodies called taste buds or taste Coblets. They
occur also. to a small extent ON tho soft pal
ate. and oven on tho surface OF tho epiElottis.
They are most conveniently studied in tho
tongue OF the rabbit. whore they exist In i'm
mense numbers AS manyas 1.7oO taste buds
have been counted on ono circumvallate pa
pilla OF an OK. The proofs that the taste buds
are tho end-oreans Of taste may bo shortly
stated as follows: The sense OF taste 10 wsnk-
ened or absent In those oreas OF mucous NOM
brane on the tongue where they are wanting
or exist only in small numbers. On tho other
hand the sense is most acute where they are
found in multltudes. Finally. a cutting OF the
glosso. .pharyngeal nerve. which Is distributed
to the area OF mucous membrane whore taste
is present. is followed by degeneration OF the
taste cells and ultimately by the entire disap-
pearance OF tho taste buds
All substances that give rise to taste are
soluble in the fluids OF the mouth. Insoluble
substances are tasteless Thus. II We touch
tho surface Of a crystal OF quartz with the
tongue. we have. it is true. a sensation OF
smooth contact, or touch. and q sensation OF
cold. because the crystal conducts heat out OF
the tongue. but there Is no sense OF taste.
Contrast this with the triple sensations OF
saline TASTE contact and coldness experienced
when We bring the tongue into contact with a
crystal OF rock salt Solution being a neces-
sary condition OF taste. We find near tho taste
organs mum morOue Small beTouS oE dlUuIulnouS
glands. tho secretions Of which assist in dis
solving sapid substances No connection has
yet been traced between the chemical COM
position OF sapid substances and the different
kinds OF taste to which they give rise. Sub
stances of very diflsrOnt chemical composition
may give rise to similar tastes For example.
sugar. acetate OF lead. and chloroform have all
O sweetish taste. although their chemical
composition is as diverse as can well be
imagined. Acids are usually sour: alkalis
havo peculiar soapy taste: salts vary much
from the sweetness OF sugar OF lead to the Bit
terness OF sulphate Of magnesia: the soluble
alkaloids. such as Quinine strychnine. and so
forth. are usually bitter: and the higher alco-
hols are more or less sweet.
The tongue. in truth. 10 the seat OF sensa-
tions that are quite unlike each other. Thus.
there are tactile sensations. as whom We touch
tho organ with pin. sensations OF pressure,
sensations OF heat and OF cold. burning or
acrid ser sations peculiar sensations excited by
the application to the tongue OF an interrupted
electrical current, and lastly. sensations oftrue
taste. We must also distinguish from these
such sensations as are called favors. expert
enced when We bring the tongue into contact
with an onion or q savory bit OF cooked neat or
fish. The latter are In reality sensations COM
pounded OF tastes and smells. and the SEN
whom We hold the nose and avoid breathing.
True tastes may be classified as sweet. bitter.
salt. sour. alkaline. and perhaps metallic. All
ofthese are specifically distinct and no doubt is
now entertained that they are due to some kind
OF action. probably chemical which they excite
in tho taste cells. While. however chemical
action probably lies at the root OF the mechan-
ism Of taste. 1t 10 remarkable that true tastes
may be excited by causes that apparently are
not chemical. Thus, smart tap on tho tongue
may excite q taste. and 1t was demonstrated
by S1lzer as long ago rs 1882 that a constant
current OF electricity causes a sensation OF
acidity at tho positive pole and OF alkalnity at
the negative pole. 1t is. OF course. possible
that the mechanical irritation In tho one case
and tho electrical current In tho other may
set FREQ chemical stimuli: but OF this there Is
no proof.
1t is well known that tho extent Of surface
acted on increases tho massiv eness OF tho sem
satlon OF tasto: on tho other hand. tho intensi-
ty is Influenced by tho degree Of concentration