With worms not only the contents of the intestines, but their ejected
matter or the castings, are generally acid. Thirty castings from
different places were tested, and with three or four exceptions were
found to be acid; and the exceptions may have been due to such castings
not having been recently ejected; for some which were at first acid, were
on the following morning, after being dried and again moistened, no
longer acid; and this probably resulted from the humus acids being, as is
known to be the case, easily decomposed. Five fresh castings from worms
which lived in mould close over the chalk, were of a whitish colour and
abounded with calcareous matter; and these were not in the least acid.
This shows how effectually carbonate of lime neutralises the intestinal
acids. When worms were kept in pots filled with fine ferruginous sand,
it was manifest that the oxide of iron, with which the grains of silex
were coated, had been dissolved and removed from them in the castings.
The digestive fluid of worms resembles in its action, as already stated,
the pancreatic secretion of the higher animals; and in these latter,
pancreatic digestion is essentially alkaline; the action will not take
place unless some alkali be present; and the activity of an alkaline
juice is arrested by acidification, and hindered by neutralization. {50}
Therefore it seems highly probable that the innumerable calciferous
cells, which are poured from the four posterior glands into the
alimentary canal of worms, serve to neutralise more or less completely
the acids there generated by the half-decayed leaves. We have seen that
these cells are instantly dissolved by a small quantity of acetic acid,
and as they do not always suffice to neutralise the contents of even the
upper part of the alimentary canal, the lime is perhaps aggregated into
concretions in the anterior pair of glands, in order that some may be
carried down to the posterior parts of the intestine, where these
concretions would be rolled about amongst the acid contents. The
concretions found in the intestines and in the castings often have a worn
appearance, but whether this is due to some amount of attrition or of
chemical corrosion could not be told. Claparede believes that they are
formed for the sake of acting as mill-stones, and of thus aiding in the
trituration of the food. They may give some aid in this way; but I fully
agree with Perrier that this must be of quite subordinate importance,
seeing that the object is already attained by stones being generally
present in the gizzards and intestines of worms.
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