ar chemical or
biological power known as _chemotaxis_, which seems to result from
variations in the surface tension of different varieties of cells,
probably caused by some substance produced by the micro-organisms.
Changes in the blood vessels then ensue, the arteries becoming dilated
and the rate of the current in them being for a time increased--_active
hyperaemia_. Soon, however, the rate of the blood flow becomes slower
than normal, and in course of time the current may cease (_stasis_), and
the blood in the vessels may even coagulate (_thrombosis_). Coincidently
with these changes in the vessels, the leucocytes in the blood of the
inflamed part rapidly increase in number, and they become viscous and
adhere to the vessel wall, where they may accumulate in large numbers.
In course of time the leucocytes pass through the vessel
wall--_emigration of leucocytes_--and move towards the seat of
infection, giving rise to a marked degree of _local leucocytosis_.
Through the openings by which the leucocytes have escaped from the
vessels, red corpuscles may be passively extruded--_diapedesis of red
corpuscles_. These processes are accompanied by changes in the
endothelium of the vessel walls, which result in an increased formation
of lymph, which transudes into the meshes of the connective tissue
giving rise to an _inflammatory oedema_, or, if the inflammation is on a
free surface, forming an _inflammatory exudate_. The quantity and
characters of this exudate vary in different parts of the body, and
according to the nature, virulence, and location of the organisms
causing the inflammation. Thus it may be _serous_, as in some forms of
synovitis; _sero-fibrinous_, as in certain varieties of peritonitis, the
fibrin tending to limit the spread of the inflammation by forming
adhesions; _croupous_, when it coagulates on a free surface and forms a
false membrane, as in diphtheria; _haemorrhagic_ when mixed with blood;
or _purulent_, when suppuration has occurred. The protective effects of
the inflammatory reaction depend for the most part upon the transudation
of lymph and the emigration of leucocytes. The lymph contains the
opsonins which act on the bacteria and render them less able to resist
the attack of the phagocytes, as well as the various protective
antibodies which neutralise the toxins. The polymorph leucocytes are the
principal agents in the process of phagocytosis (p. 22), and together
with the other forms of phagocytes t