acids. We shall have to recur to this subject in our fifth
chapter, and I need here only say that these acids act strongly on
carbonate of lime. The half-decayed leaves which are swallowed in
such large quantities by worms would, therefore, after they have
been moistened and triturated in the alimentary canal, be apt to
produce such acids. And in the case of several worms, the contents
of the alimentary canal were found to be plainly acid, as shown by
litmus paper. This acidity cannot be attributed to the nature of
the digestive fluid, for pancreatic fluid is alkaline; and we have
seen that the secretion which is poured out of the mouths of worms
for the sake of preparing the leaves for consumption, is likewise
alkaline. The acidity can hardly be due to uric acid, as the
contents of the upper part of the intestine were often acid. In
one case the contents of the gizzard were slightly acid, those of
the upper intestines being more plainly acid. In another case the
contents of the pharynx were not acid, those of the gizzard
doubtfully so, while those of the intestine were distinctly acid at
a distance of 5 cm. below the gizzard. Even with the higher
herbivorous and omnivorous animals, the contents of the large
intestine are acid. "This, however, is not caused by any acid
secretion from the mucous membrane; the reaction of the intestinal
walls in the larger as in the small intestine is alkaline. It must
therefore arise from acid fermentations going on in the contents
themselves . . . In Carnivora the contents of the coecum are said
to be alkaline, and naturally the amount of fermentation will
depend largely on the nature of the food." {26}

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