e trabecular framework of the portion of bone affected.
Clinically, carious bone yields a soft grating sensation under the
pressure of the probe. The macerated bone presents a rough, eroded
surface.

The term _dry caries_ (_caries sicca_) is applied to that variety which
is unattended with suppuration.

_Necrosis_ is the term applied to the death of a tangible portion of
bone, and the dead portion when separated is called a _sequestrum_. The
term _exfoliation_ is sometimes employed to indicate the separation or
throwing off of a superficial sequestrum. The edges and deep surface of
the sequestrum present a serrated or worm-eaten appearance due to the
process of erosion by which the dead bone has been separated from the
living.

BACTERIAL DISEASES

The most important diseases in this group are the pyogenic, the
tuberculous, and the syphilitic.

PYOGENIC DISEASES OF BONE.--These diseases result from
infection with pyogenic organisms, and two varieties or types are
recognised according to whether the organisms concerned reach their seat
of action by way of the blood-stream, or through an infection of the
soft parts in contact with the bone.

INFECTIONS THROUGH THE BLOOD-STREAM

#Diseases caused by the Staphylococcus Aureus.#--As the majority of
pyogenic diseases are due to infection with the staphylococcus aureus,
these will be described first.

#Acute osteomyelitis# is a suppurative process beginning in the marrow
and tending to spread to the periosteum. The disease is common in
children, but is rare after the skeleton has attained maturity. Boys are
affected more often than girls, in the proportion of three to one,
probably because they are more liable to exposure, to injury, and to
violent exertion.

_Etiology._--Staphylococci gain access to the blood-stream in various
ways, it may be through the skin or through a mucous surface.

Such conditions as, for example, a blow, some extra exertion such as a
long walk, or exposure to cold, as in wading, may act as localising
factors.

The long bones are chiefly affected, and the commonest sites are: either
end of the tibia and the lower end of the femur; the other bones of the
skeleton are affected in rare instances.

_Pathology._--The disease commences and is most intense in the marrow of
the ossifying junction at one end of the diaphysis; it may commence at
both ends simultaneously--_bipolar osteomyelitis_; or, commencing at one
end, may spread to the oth