mallpox in members of the
human family is well known. The immunity which such vaccination confers
upon the human subject has led many writers to assert that cowpox is simply
a modified form of smallpox, whose harmless attack upon the human system is
owing to a certain attenuation derived during its passages through the
system of the cow or horse. The results of numerous experiments which have
been carried out for the purpose of determining the relationship existing
between variola of the human and bovine families seem to show, however,
that although possessing many similar characteristics, they are
nevertheless distinct, and that in spite of repeated inoculations from
cattle to man, and vice versa, no transformation in the real character of
the disease ever takes place.

_Symptoms._--The disease appears in four to seven days after natural
infection, or may evince itself in two or three days as the result of
artificial inoculation. Young milch cows are most susceptible to an attack,
but older cows, bulls, or young cattle are by no means immune. The attack
causes a slight rise in temperature, which is soon followed by the
appearance of reddened, inflamed areas, principally upon the teats and
udder, and at times on the abdominal skin or the skin of the inner surface
of the thighs. In a few cases the skin of the throat and jaws has been
found similarly involved. If the affected parts are examined on the second
day after the establishment of the inflammation numerous pale-red nodules
will be found, which gradually expand until, within a few days, they reach
a diameter of one-half inch or even larger. At this period the tops of the
nodules become transformed into vesicles which are depressed in the center
and contain a pale, serous fluid. They usually reach their maturity by the
tenth day of the course of the disease and are then the size of a bean.
From this time the contents of the vesicles become purulent, which requires
about three days, when the typical pox pustule is present, consisting of a
swelling with broad, reddened base, within which is an elevated, conical
abscess varying from the size of a pea to that of a hazelnut.

The course of the disease after the full maturity of the pustule is rapid
if outside interference has not caused a premature rupture of the small
abscess at the apex of the swelling. The pustules gradually become darker
colored and drier until nothing remains but a thick scab, which at last
falls of