e drawn between secondary and tertiary lesions.

_The primary period_ embraces the interval that elapses between the
initial infection and the first constitutional manifestations,--roughly,
from four to eight weeks,--and includes the period of incubation, the
development of the primary sore, and the enlargement of the nearest
lymph glands.

_The secondary period_ varies in duration from one to two years, during
which time the patient is liable to suffer from manifestations which are
for the most part superficial in character, affecting the skin and its
appendages, the mucous membranes, and the lymph glands.

_The tertiary period_ has no time-limit except that it follows upon the
secondary, so that during the remainder of his life the patient is
liable to suffer from manifestations which may affect the deeper tissues
and internal organs as well as the skin and mucous membranes.

#Primary Syphilis.#--_The period of incubation_ represents the interval
that elapses between the occurrence of infection and the appearance of
the primary lesion at the site of inoculation. Its limits may be stated
as varying from two to six weeks, with an average of from twenty-one to
twenty-eight days. While the disease is incubating, there is nothing to
show that infection has occurred.

_The Primary Lesion._--The incubation period having elapsed, there
appears at the site of inoculation a circumscribed area of infiltration
which represents the reaction of the tissues to the entrance of the
virus. The first appearance is that of a sharply defined papule, rarely
larger than a split pea. Its surface is at first smooth and shiny, but
as necrosis of the tissue elements takes place in the centre, it becomes
concave, and in many cases the epithelium is shed, and an ulcer is
formed. Such an ulcer has an elevated border, sharply cut edges, an
indurated base, and exudes a scanty serous discharge; its surface is at
first occupied by yellow necrosed tissue, but in time this is replaced
by smooth, pale-pink granulation tissue; finally, epithelium may spread
over the surface, and the ulcer heals. As a rule, the patient suffers
little discomfort, and may even be ignorant of the existence of the
lesion, unless, as a result of exposure to mechanical or septic
irritation, ulceration ensues, and the sore becomes painful and tender,
and yields a purulent discharge. The primary lesion may persist until
the secondary manifestations make their appearance, that