One of the digestive processes is the conversion of starch into sugar.
The relation of these two bodies is a very simple one, starch being
readily converted into sugar by the addition to its molecule of a
molecule of water. The change can not be produced by simply adding
starch to water, but the water must be introduced into the starch
molecule. This change can be brought about in a variety of ways, and is
undoubtedly effected by the forces of chemical affinity. Chemists have
found simple methods of producing this chemical union, and the
manufacture of sugar out of starchy material has even become something
of a commercial industry. One of the methods by which this change can be
produced is by adding to the starch, along with some water, a little
saliva. The saliva has the power of causing the chemical change to occur
at once, and the molecule of water enters into the starch molecule and
forms sugar. Now we do not understand how this saliva possesses this
power to induce the chemical change. But apparently the process is of
the simplest character and involves no greater mystery than chemical
affinity. We know that the saliva contains a certain material called a
ferment, which is the active agent in bringing about the change. This
ferment is not alive, nor does it need any living environment for its
action. It can be separated from the saliva in the form of a dry
amorphous powder, and in this form can be preserved almost
indefinitely, retaining its power to effect the change whenever put
under proper conditions. The change of starch into sugar is thus a
simple chemical change occurring under the influence of chemical
affinity under certain conditions. One of the conditions is the presence
of this saliva ferment. If we can not exactly understand how the ferment
produces this action, neither do we exactly understand how a spark
causes a bit of gunpowder to explode. But we can not doubt that the
latter is a purely natural result of the relation of chemical and
physical forces, and there is no more reason for doubting it in the