isible sign of the disease appears at the site of inoculation,
and is known as _the primary lesion_. Those who have thus acquired the
disease may transmit it to their offspring, who are then said to suffer
from _inherited syphilis_.

#The Virus of Syphilis.#--The cause of syphilis, whether acquired or
inherited, is the organism, described by Schaudinn and Hoffman, in 1905,
under the name of _spirochaeta pallida_ or _spironema pallidum_. It is a
delicate, thread-like spirilla, in length averaging from 8 to 10
[micron] and in width about 0.25 [micron], and is distinguished from
other spirochaetes by its delicate shape, its dead-white appearance,
together with its closely twisted spiral form, with numerous undulations
(10 to 26), which are perfectly regular, and are characteristic in that
they remain the same during rest and in active movement (Fig. 36). In a
fresh specimen, such as a scraping from a hard chancre suspended in a
little salt solution, it shows active movements. The organism is readily
destroyed by heat, and perishes in the absence of moisture. It has been
proved experimentally that it remains infective only up to six hours
after its removal from the body. Noguchi has succeeded in obtaining pure
cultures from the infected tissues of the rabbit.

[Illustration: FIG. 36.--Spirochaeta pallida from scraping of hard
Chancre of Prepuce. x 1000 diam. Burri method.]

The spirochaete may be recognised in films made by scraping the deeper
parts of the primary lesion, from papules on the skin, or from blisters
artificially raised on lesions of the skin or on the immediately
adjacent portion of healthy skin. It is readily found in the mucous
patches and condylomata of the secondary period. It is best stained by
Giemsa's method, and its recognition is greatly aided by the use of the
ultra-microscope.

The spirochaete has been demonstrated in every form of syphilitic lesion,
and has been isolated from the blood--with difficulty--and from lymph
withdrawn by a hollow needle from enlarged lymph glands. The saliva of
persons suffering from syphilitic lesions of the mouth also contains the
organism.

[Illustration: FIG. 37.--Spirochaeta refrigerans from scraping of Vagina.
x 1000 diam. Burri method.]

In tertiary lesions there is greater difficulty in demonstrating the
spirochaete, but small numbers have been found in the peripheral parts of
gummata and in the thickened patches in syphilitic disease of the aorta.
Noguchi