so that the air may come in while they are sucking. Not only do
animals know the food that will suit them best, but they find out the
most suitable remedies when they are ill, and constantly form a
correct diagnosis of their malady with a therapeutical knowledge
which they cannot possibly have acquired. Dogs will often eat a
great quantity of grass--particularly couch-grass--when they are
unwell, especially after spring, if they have worms, which thus pass
from them entangled in the grass, or if they want to get fragments of
bone from out of their stomachs. As a purgative they make use of
plants that sting. Hens and pigeons pick lime from walls and
pavements if their food does not afford them lime enough to make
their eggshells with. Little children eat chalk when suffering from
acidity of the stomach, and pieces of charcoal if they are troubled
with flatulence. We may observe these same instincts for certain
kinds of food or drugs even among grown-up people, under
circumstances in which their unconscious nature has unusual power;
as, for example, among women when they are pregnant, whose capricious
appetites are probably due to some special condition of the foetus,
which renders a certain state of the blood desirable. Field-mice
bite off the germs of the corn which they collect together, in order
to prevent its growing during the winter. Some days before the
beginning of cold weather the squirrel is most assiduous in
augmenting its store, and then closes its dwelling. Birds of passage
betake themselves to warmer countries at times when there is still no
scarcity of food for them here, and when the temperature is
considerably warmer than it will be when they return to us. The same
holds good of the time when animals begin to prepare their winter
quarters, which beetles constantly do during the very hottest days of
autumn. When swallows and storks find their way back to their native
places over distances of hundreds of miles, and though the aspect of