milk has become a constant
function in the animal economy of the tribe; it has been rendered
such by the practice, continued through long series of generations,
of continuing to draw milk long after the period when it would be
wanted for the calf; the teats of the cow are larger than in
proportion, and the secretion is perpetual. In Columbia, the
practice of milking cows was laid aside, owing to the great extent
of farms and other circumstances. 'In a few generations,' says M.
Roulin, 'the natural structure of parts, and withal, the natural
state of the function, has been restored. The secretion of milk in
the cow of this country is only an occasional phenomenon, and
contemporary with the actual presence of the calf. If the calf
dies, the milk ceases to flow, and it is only by keeping him with
his dam by day, that an opportunity of obtaining milk from cows by
night can be found.' This testimony is important, by the proof
which it affords that the permanent production of milk in the
European breeds of cows is a modified function of the animal
economy, produced by an artificial habit continued through several
generations. Two other very important observations made by M.
Roulin in South America, were pointed out by M. Geoffrey St Hilaire
in his report to the Academy of Sciences. They refer to the fact of
the hereditary transmission of habits originally impressed with
care and art upon the ancestors. Of this fact I shall adduce other
examples in the sequel; at present I only advert to M. Roulin's
observations. The horses bred in the grazing farms on the
table-land of the Cordillera, are carefully taught a peculiar pace,
which is a sort of running amble. This is not their natural mode of
progression, but they are inured to it very early, and the greatest
pains are taken to prevent them from moving in any other gait. In
this way the acquired habit becomes a second nature. It happens
occasionally that such horses, becoming lame, are no longer fit for
use; it is then customary to let them loose, if they happen to be
well-grown stallions, into the pasture grounds. It is constantly
observed that these horses become the sires of a race to which the
ambling pace is natural, and requires no teaching. The fact is so
well known, that such colts have received a part