Full resolution (JPEG) - On this page / på denna sida - III. The Carbohydrates
<< prev. page << föreg. sida << >> nästa sida >> next page >>
Below is the raw OCR text
from the above scanned image.
Do you see an error? Proofread the page now!
Här nedan syns maskintolkade texten från faksimilbilden ovan.
Ser du något fel? Korrekturläs sidan nu!
This page has never been proofread. / Denna sida har aldrig korrekturlästs.
CHAPTER III.
THE CARBOHYDRATES.
We designate by this name bodies which are especially abundant
in the plant kingdom. As the protein bodies form the chief portion
of the solids in animal tissues, so the carbohydrates form the chief por-
tion of the dry substance of the plant structure. They occur in the
animal kingdom only in proportionately small quantities, either free .or
in combination with more complex molecules, forming compound pro-
teins. Carbohydrates are of extraordinarily great importance as food
for both man and animals.
The carbohydrates contain only carbon, hydrogen, and oxygen. The
last two elements occur, as a rule, in the same proportion as they do in
water, namely, 2:1, and this is the reason why the name carbohydrates
has been given to them. This name is not quite pertinent, if strictly
considered, because we not only have bodies, such as acetic acid and
lactic acid, which are not carbohydrates and still have their oxygen and
hydrogen in the same proportion as in water, but we also have a sugar
(the methyl pentoses, C6H12O5) which has these two elements in another
proportion. At one time it was thought possible to characterize as
carbohydrates those bodies which contained 6 atoms of carbon, or a
multiple, in the molecule, but this is not considered tenable at the present
time. We have true carbohydrates containing less than 6, and also those
containing 7, 8, and 9 carbon atoms in the molecule.
The carbohydrates have no properties or characteristics in general
which differentiate them from other bodies; on the contrary, the various
carbohydrates are in many cases very different in their external prop-
erties. Under these circumstances it is very difficult to give a positive
definition for the carbohydrates.
From a chemical standpoint we can say that all carbohydrates are
aldehyde or ketone derivatives of polyhydric alcohols. The simplest
carbohydrates, the simple sugars or monosaccharides, are either alde-
hyde or ketone derivatives of such alcohols, and the more complex
carbohydrates seem to be derived from these by the formation of anhy-
drides. It is a fact that the more complex carbohydrates yield two
-or even more molecules of the simple sugars when made to undergo
hydrolytic splitting.
196
<< prev. page << föreg. sida << >> nästa sida >> next page >>
