each
surmounted by a minute blister (vesicle); (d) inflammation with a
similar eruption but with larger blisters, like half a pea and upwards
(bullae); (e) inflammation with a similar eruption, but with a small
sac of white, creamy pus on the summit of each elevation (pustules);
(f) the formation of pustules implicating the superficial layer of the
true skin, a small portion of which dies and is thrown off as a slough,
or "core" (boils); (g) the formation of round, nodular, transient
swellings in the true skin (tubercles); and (h) the excessive
production of scales, or dandruff (scaly or squamous affections).

(2) Diseases in which there are only deranged sensations of itching,
heat, tenderness, etc. (neurosis).

(3) Diseased growths, such as warts, callosities, horny growths, cancer,
etc.

(4) Diseases from parasites, animal and vegetable.

(5) Diseases connected with a specific poison, such as horsepox,
erysipelas, anthrax, farcy, or cutaneous glanders, etc.

(6) Physical injuries, like wounds, burns, scalds, etc.

CONGESTION (RED EFFLORESCENCE, OR ERYTHEMA).

This is a congested or slightly inflamed condition of the skin,
unattended with any eruption. The part is slightly swollen, hot, tender,
or itchy, and dry, and if the skin is white there is redness. The
redness is effaced by pressure, but reappears instantly when it is
removed. Except in transient cases the hairs are liable to be shed. It
may be looked on as the first stage of inflammation, and therefore when
it becomes aggravated it may merge in part or in whole into a papular,
vesicular, or pustular eruption.

Erythema may arise from a variety of causes, and is often named in
accordance with its most prominent cause. Thus the chilling, or partial
freezing, of a part will give rise to a severe reaction and congestion.
When snowy or icy streets have been salted this may extend to severe
inflammation, with vesicles, pustules, or even sloughs of circumscribed
portions of the skin of the pastern (chilblain, frost-bite). Heat and
burning have a similar effect, and this often comes from exposure to the
direct rays of the sun. The skin that does not perspire is the most
subject, and hence the white face or white limb of a horse becoming
dried by the intensity of the sun's rays often suffers to the exclusion
of the rest of the body (white face and foot disease). The febrile state
of the general system is also a potent cause; hence the white-skinned
horse i