to hypoxanthin
{|Oxidases |Lungs, liver, |Changes hypoxanthin
{| | muscles, etc. | to xanthin and to
{| | | uric acid
==============+===================+==================+===================

~Classification of Enzymes.~--Sherman classifies the enzymes of the
body according to their effects:

1. The hydrolytic enzymes:

(a) Proteolytic or protein-splitting enzymes.

(b) Lipolytic or fat-splitting enzymes.

(c) Amylolytic or starch-splitting enzymes.

(d) Sugar-splitting enzymes.

2. The coagulating enzymes, such as thrombin or thrombase (the fibrin
ferment) and rennin, which causes the clotting of milk.

3. The oxidizing enzymes or oxidases (which, if the oxidation be
accompanied by a splitting off of amino groups, may be called
"deaminizing" enzymes).

4. The reducing enzymes or "reductases."

5. Those which produce carbon dioxide without the use of free
"deamidizing" oxygen, such as zymase of yeast.

6. Enzymes causing the breaking down of a larger into a smaller
molecule of the same composition, as in the production of lactic acid
from glucose.

DIGESTION (CHEMICAL)

~Salivary Digestion.~--The table shows that enzymic action begins in
the mouth. ~Saliva~, the characteristic secretion of this region,
contains the enzyme ptyalin which exerts its influence upon the
starches and dextrins. The food mass remains in the mouth for so short
a time, however, that a very small percentage of the starch is changed
to maltose under salivary digestion. The action of ptyalin, however,
continues in the fundus of the stomach until stopped by the acid in
the gastric juice.

~Gastric Digestion.~--The conditions existing in this region of the
gastric organ of digestion are particularly favorable to the
continuance of salivary digestion on account of the neutral character
of the juices secreted by the cells there, and because there is so
little movement taking place. The cells in the middle region,
however, secrete a fluid rich in acid, and as the food mass is
gradually pushed forward by the contraction of the stomach walls into
this portion of the stomach, further conversion of starch and dextrin
to maltose is checked. Gastric juice is secreted by cells situated in
all parts of the stomach. The character of the secretions differs in
different parts of the organ. However, that in the fundus is neutral