excretory ducts of the mucous glands; the thinner
part of this secretion exhales, and the remainder becomes inspissated, and
lodges in the duct; the extremity of which becomes black by exposure to the
air.

M. M. They may be pressed out by the finger-nails. Warm water. Ether
frequently applied. Blister on the part?

10. _Maculae cutis fulvae._ Morphew or freckles. Tawny blotches on the skin
of the face and arms of elderly people, and frequently on their legs after
slight erysipelas. The freckles on the face of younger people, who have red
hair, seem to be a similar production, and seem all to be caused by the
coalescence of the minute arteries or capillaries of the part. In a scar
after a wound the integument is only opake; but in these blotches, which
are called morphew and freckles, the small vessels seem to have become
inactive with some of the serum of the blood stagnating in them, from
whence their colour. See Class III. 1. 2. 12.

M. M. Warm bathing. A blister on the part?

11. _Canities._ Grey hair. In the injection of the vessels of animals for
the purposes of anatomical preparations, the colour of the injected fluid
will not pass into many very minute vessels; which nevertheless uncoloured
water, or spirits, or quicksilver will permeate. The same occurs in the
filtration of some coloured fluids through paper, or very fine sand, where
the colouring matter is not perfectly dissolved, but only diffused through
the liquid. This has led some to imagine, that the cause of the whiteness
of the hair in elderly people may arise from the diminution, or greater
tenuity, of the glandular vessels, which secrete the mucus, which hardens
into hair; and that the same difference of the tenuity of the secerning
vessels may possibly make the difference of colour of the silk from
different silk-worms, which is of all shades from yellow to white.

But as the secreted fluids are not the consequence of mechanical
filtration, but of animal selection; we must look out for another cause,
which must be found in the decreasing activity of the glands, as we advance
in life; and which affects many of our other secretions as well as that of
the mucus, which forms the hair. Hence grey hairs are produced on the faces
of horses by whatever injures the glands at their roots, as by corrosive
blisters; and frequently on the human subject by external injuries on the
head; and sometimes by fevers. And as the grey colour of hair consists in
its