The rôle of =microbes= in inflammation is much greater than was formerly
supposed. It is now demonstrated that a large class of inflammations are
directly caused by the colonization of microbes in the tissue and by the
local irritation caused by their ptomaines and toxins. We must also
admit the direct action of the latter on the heat producing and
vaso-motor nervous centres, as a factor more or less potent in different
cases in the causation and maintenance of inflammation. No less
important is the relation of the microbe to the migration of the
globules and the subsequent results of the inflammation. This influence
microbes share with certain chemical agents. Migration may be greatly
checked even in inflamed parts by the hypodermic or intravenous
injection of sulphate of quinia, eucalyptol, salicylic acid, or
iodoform. Some have thought these acted by a chemiotactic attraction,
but quinia is otherwise found to repel the leucocytes. Their action on
the leucocytes or capillary walls is problematic.
=Chemiotaxis= is that power by which a microbe or any element attracts
or repels the leucocytes. When it attracts the chemiotaxis is said to be
positive, when it repels it is negative. Among negative chemiotactic
agents are quinia, solutions of sodium chloride (10%), and potassium
salts, lactic acid, alcohol (10%), chloroform, glycerine, jequirity, and
bile. To some agents, (creatine, creatinine, allantoin, peptone,
phlorydzine,) leucocytes are indifferent. To gluten, wheat casein, pea
legumin and the great majority of pathogenic microbes, leucocytes are
positively attracted. As microbes exercise a great influence in
producing local inflammation, so they are important factors in procuring
an abundant emigration of leucocytes. Some of the most fatal of
microbian diseases, like fowl cholera, repel leucocytes, and the benefit
of their defensive work is to a large extent lost. The toxins of the
chemiotactic microbe filtered from the bacteria exert the same influence
as the living bacteria, as shown by Gabritchevski, Massart and Bordet.
But chemiotaxis may be exerted from within the bloodvessel as well as
from without. Bouchard, Massart and Bordet have shown that a tube
containing a culture of bacillus pyocyanus, introduced beneath the skin
of a rabbit attracts in a few hours a great number of leucocytes. But
if, immediately after its introduction, ten cubic centimetres of a
sterilized culture of the same bacillus are injected into a vein, very
few leucocytes enter the tube inserted under the skin. The chemiotaxis
seems to operate in this case from within the blood, and the desires of
the leucocytes are satisfied without leaving the vessel. It would seem
that in such cases the migration and protective work of the leucocytes
is best exerted at the outset of the illness and before the toxic
products have been poured into the blood in any quantity, whereas in the
advanced stages when the blood is charged with ptomaines and toxins
migration and phagocytosis would be likely to be limited and
ineffective. The same consideration would forbid the use of drugs that
check migration in all cases of attacks by microbes for which leucocytes
have a positive chemiotaxis.
=Phagocytosis= is the act by which the leucocytes englobe and dissolve
the invading microbe. By its amœboid movement the leucocyte flows
around, and envelopes the microbe for which it has a positive
chemiotaxis, and then begins the struggle of vitality between the two
living germs. If the poison (leucomaine antitoxin,) and digestive
ferment (enzyme) of the leucocytes are more deadly to the invading germ,
than its ptomaines, toxins and enzymes are to the leucocyte, the white
cell comes off the victor, and recovery takes place, but if the converse
obtains the triumph is on the side of the microbe. As a rule much
depends on the more or less deadly nature of the products of the
invading microbe, on the numbers of the germ, the rapidity of its
proliferation, and the consequent amount of its toxic products thrown
into the system, on the one hand: And on the other the potency of the
chemiotaxis of the leucocyte for the invading germ, the number of white
cells that emigrate into the inflamed tissue and engage in the work of
phagocytosis, and on whether the particular animal system and its white
cells have sustained a previous attack by the same germ and has thereby
been educated to produce a greater amount of the defensive proteids
(leucomaine, antitoxin, enzyme) than it naturally would (acquired
immunity).
Even with an abundant emigration of the leucocytes into the inflamed or
invaded tissue, a number, greater or less, are usually destroyed by the
bacterial poisons and pass into degeneration or liquefaction, as in the
formation of pus, and yet the attacking germ may be overcome, destroyed
and devoured by the rapidly increasing survivors. In general terms the
migration of the cells is in inverse ratio to the susceptibility of the
animal to the microbe or the disease which it causes.
The positive and negative chemiotaxis, which determine phagocytosis or
prevent it, may be seen in the action of the leucocytes toward the germs
of two diseases, to one of which the animal is susceptible and to the
other of which it is not. Thus the leucocytes of the pigeon take in the
bacillus anthracis and suffer nothing apparently, whereas the same white
cells of the dove are repelled by the bacteria of fowl cholera which are
not therefore found in their interior.
The leucocytes that migrate from the bloodvessels are in the main, the
most numerous, (the neutrophile or polynuclear) form; the mononuclear
leucocytes with horseshoe shaped nucleus also migrate but in much fewer
numbers and are as a rule less occupied in phagocytosis. At the same
time, these two forms may show each a preference for a particular
microbe, the polynuclear cell sometimes devouring one which the
mononuclear cell rejects, and the mononuclear cell taking in one which
the polynuclear refuses.
The small round white cells (lymphocytes) and the eosinophile leucocytes
take no prominent part in phagocytosis.