of the disease.

_Cause_.--Anthrax is caused by a rod-shaped, spore-producing microorganism,
_Bacillus anthracis_ (Fig. 103). It gains entrance to the body by way of
the intestinal tract, lungs and air-passages and the skin. The bites of
insects play an important part in the distribution of the disease in some
localities, but the most common method of infection is by way of the
digestive tract, through eating and drinking food and water contaminated
with the anthrax germs. The spores of the _B. anthracis_ are very resistant
to changes in temperature and drying. They may live for years in rich,
moist inundated soils. River-bottom and swampy lands that have become
infected with discharges from the bodies of animals sick with anthrax, and
by burying the carcasses of animals that have died of this disease, retain
the infection for many years. Anthrax is very widely distributed. It is the
most prevalent in the southern portion of the United States, especially the
lower portion of the Mississippi Valley.

[Illustration: FIG. 103.--_Bacillus anthracis_.]

_The symptoms vary in different cases_, depending on the organs affected,
and the virulence and amount of virus introduced. The _apoplectic form_ is
very acute. The disease sets in suddenly; the animal trembles, staggers,
falls and dies in a convulsion. Blood may be discharged from the nose and
with the urine and faeces.

In the _abdominal form_, abdominal pain, diarrhoea, prolapse of the rectum,
bloating and doughy swellings in the region of the abdomen occur.

In the _thoracic form_, the symptoms are bloody discharge from the
nostrils, salivation, rapid, difficult breathing and swelling in the region