Science Notes
BY WILLIAM G. HAYNES.
The Unsolved Mystery of Why the
Stomach Does Not Digest Itself.
It has often been questioned why
the stomach does not digest itself.
Proteids in the shape of tissues of
other animals rapidly dissolve when
introduced into the gastric juice but
the stomach tissue itself is never at
tacked by its own gastric juice.
Among the various reasons that have
been suggested are the protective
influence of the mucous secreted
along the digestive canal, and the
existence of anti-enzymes, which
counteract the activity of the diges
tive juices. Neither of these theories
has, however, been accepted as cap
able of explaining the complete and
continued immunity of the digestive
tract to digestion. It cannot even be
asserted that it is simply because
these tissues are alive that they are
thus protected, since the living mu
cous membrane of the urinary blad
der. for example, is dissolved by the
pancreatic or gastric juice of an ani
mal of the same species. Even the
living mucous membrane of the intes
tine is apparently digested by the gas
tric juice of the animal to which it
belongs if food is not introduced at
the same time. The protection of liv
ing tissues to digest fluids is thus lim
ited. On the other hand, however,
some aquatic forms of life, such as
protozoans, worms, crustaceans and
insects have been kept alive at times
for a month, in a solution of trypsin
that would quickly have dissolved a
mass of dead protein.
So a correspondent to the Journal
of the American Medical Association
for July 18, 1914, concludes that the
stomach is an active gastric secretion
and of the intestinal mucous mem
brane to pancreatic juice still remains
a mystery. Some unknown protec
tive power of adaptation under cer
tain circumstances must be admitted
as one of the innumerable factors of
evolution of which we are still igno
rant— H. W. S. in Science Conspec
tus.
Limits of Experimental Investigation.
The problem as to where the limits
accessible to experimental investiga
tion are reached has ever been one
appealing to the human mind. While
it would be premature to answer the
question in an absolute manner, as
signing to scientific work a boundary
never to be exceeded, the limits cor
responding to the present state of
science can be ascertained with a high
degree of accuracy.
The lowest temperature obtainable
by artificial means, until twenty years
ago was —87 deg. Cent., liquid car
bonic acid being used for its produc
tion. When then Prof. Linde, by the
construction of hiB refrigerating ma
chine, opened up new fields to cold
storage scientists succeeded in work
ing at temperatures as low as —190 to
—200 deg. Cent. Since hydrogen does
not boil above a temperature of, say,
—253 deg. Cent, the use of this lique
fied gas allowed even lower tempera
tures to be reached, while helium, the
boiling point of which lies at —269
deg. Cent., quite recently enabled Dr.
Kamerlingh-Onnes nearly to reach
the temperature of absolute zero.
As pointed out by Prof. Kurt Ardnt,
in a lecture held at the Society of Ger
man Chemists, the temperature of the
electric arc forms a counterpart to
this lowest temperature reached by
artificial means. It is true that the
temperature of the electric arc is any
thing but uniform, 3,000 to 4,000 deg.
Cent., being recorded at some places,
while others show temperatures as
low as 1,000 deg. Cent. Whenever
constant temperatures are to be used
for purposes of scientific investigation
they must therefore be produced by
means of electric radiators. Thin nick
el wires traversed by electric currents
will be sufficient in this connection up
to 1,000 degrees, while Heraeus’ platl
num furnaces are used above this lim
it, and iridium metal (which it is true,
cannot be drawn out into wires or
hammered) between 1,500 and 2,000
deg. Cent. Since the melting point
of tungsten is as high as 3,000 deg.
Cent., its use allows even higher tem
peratures to be reached, though on ac
count of its sensitiveness to atmos
pheric oxygen, this element must he
kept in the vacuum. The highest
temperatures (up to 2,700 deg. Cent.)
tehrefore are preferably produced by
the aid of carbon resistances used in
connection with several types of elec
tric furnaces.
The most varied instruments are
used to gauge the lowr and high tem
peratures thus produced. Degrees of
cold can be determined with mercury
thermometers only as far as —38 deg.
Cent., which is the freezing point of
mercury. Liquid thermometers, filled
with liquids, such as pentane, will suf
fice down to temperatures of, say,
—100 deg. Cent., when pentane be
comes plastic. Resistance themom
eters, designed by William Siemens
(and based on the increasing electri
cal conductivity of platinum with de
creasing temperatures) serve for the
measuring of temperatures still low
er. The relation between temperature
and the resistance of platinum being
knowi\, temperatures above j—1,000
deg. Cent, can be gauged by this
means. Thermo-electric pyrometers
(based on the production of electric
currents by heating the contact be
tween certain metals and metal al
loys) are used in determining temper
atures between 500 and 1,500 degrees,
while optical pyrometers—in connec
tion with which the surface bright
ness of incandescent bodies is deter
mined by an optical process—must be
resoted to in the case of temperatures
even higher than 1,500 degrees. The
greater the brightness of an incan
descent body, the higher, of course,
will be its temperature.
As regards, next, the measuring of
time, stop watches will be sufficient
for intervals of, say, one-fifth of a sec
ond as a minimum. Any more rapid
phenomena must be allowed to rec
ord themselves of their own accord.
In the case, for instance, of explosive
phenomena, the pressure of explosion
is made to displace a minute mirror,
whence a reflected beam of light falls
on a revolving drum coated with pho
tographic paper. The displacement of
the mirror, as produced by the pres
sure of explosion, is thus recorded
photographically, instervals of, say,
1-50,000 second being gauged in this
way.
While ordinary chemical scales, of
cause, insure an accuracy of 1-10 mil
ligramme, extra-sensitive weighing
machines, such as those used in com
paring standards of weight, allow dif
ferences as small as 1-500 milli
gramme to be ascertained.
Especially sensitive, however, are
the processes used in determining
lengths, the interferometer allowing
the three-hundredth part of a mil
lion; n of a millometer to he gauged, a
length far too small to be conceived
by the human mind. The ultra my
croscope, finally, enables the one-hun
dred thousandth part of a millimeter
to be visualized in gold solutions.—
Scientific American Supplement.
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