We proceed now to consider the most important function of the stomach, by which the assimilation of the food is begun. But before that function can be well understood, it is necessary to make a few remarks on the influence of water, in modifying the intimate constitution and the peculiar properties of alimentary substances. We have intentionally delayed these remarks, in order that in this place the chemical influence of water might be more strikingly exemplified.

Water enters into the composition of most organized bodies in two separate forms; which must be clearly distinguished, and which it is requisite that the reader should always bear in mind. Water may constitute an essential element of a substance, as of sugar or of starch in their dryest states; in which case, the water cannot be disunited without destroying the compound: or water may constitute an accidental ingredient of a substance, as of sugar or of starch in their moist states; in which case more or less of the water may frequently be removed, without destroying the essential properties of the compound. Now, a very large number of organized bodies, (perhaps all those to which our present enquiry relates) contain water in both these forms; both as an essential element, and as an accidental ingredient; and in most instances, it is impossible to discriminate between the water which is essential, and that which is accidental.