chemical agents, retain their
vitality in a dry condition, and even survive boiling for five minutes.

The organism does not readily establish itself in the human body, and
seems to flourish best when it finds a nidus in necrotic tissue and is
accompanied by aerobic organisms, which, by using up the oxygen in the
tissues, provide for it a suitable environment. The presence of a
foreign body in the wound seems to favour its action. The infection is
for all practical purposes a local one, the symptoms of the disease
being due to the toxins produced in the wound of infection acting upon
the central nervous system.

The toxin acts principally on the nerve centres in the spinal medulla,
to which it travels from the focus of infection by way of the nerve
fibres supplying the voluntary muscles. Its first effect on the motor
ganglia of the cord is to render them hypersensitive, so that they are
excited by mild stimuli, which under ordinary conditions would produce
no reaction. As the toxin accumulates the reflex arc is affected, with
the result that when a stimulus reaches the ganglia a motor discharge
takes place, which spreads by ascending and descending collaterals to
the reflex apparatus of the whole cord. As the toxin spreads it causes
both motor hyper-tonus and hyper-excitability, which accounts for the
tonic contraction and the clonic spasms characteristic of tetanus.

[Illustration: FIG. 26.--Bacillus of Tetanus from scraping of a wound of
finger, x 1000 diam. Basic fuchsin stain.]

#Clinical Varieties of Tetanus.#--_Acute_ or _Fulminating
Tetanus_.--This variety is characterised by the shortness of the
incubation period, the rapidity of its progress, the severity of its
symptoms, and its all but universally fatal issue in spite of
treatment, death taking place in from one to four days. The
characteristic symptoms may appear within three or four days of the
infliction of the wound, but the incubation period may extend to three
weeks, and the wound may be quite healed before the disease declares
itself--_delayed tetanus_. Usually, however, the wound is inflamed and
suppurating, with ragged and sloughy edges. A slight feverish attack may
mark the onset of the tetanic condition, or the patient may feel
perfectly well until the spasms begin. If careful observations be made,
it may be found that the muscles in the immediate neighbourhood of the
wound are the first to become contracted; but in the majority of
instances th