ted to some particular part of the body,
and the symptoms are due to toxins which are absorbed from it. Thus in
cholera the bacteria are practically confined to the intestine, in
diphtheria to the region of the false membrane, in tetanus to some wound.
In the last-mentioned disease even the local multiplication depends upon
the presence of other bacteria, as the tetanus bacillus has practically no
power of multiplying in the healthy tissues when introduced alone.

[Sidenote: Tissue changes.]

The effects produced by bacteria may be considered under the following
heads: (1) tissue changes produced in the vicinity of the bacteria, either
at the primary or secondary foci; (2) tissue changes produced at a distance
by absorption of their toxins; (3) symptoms. The changes in the vicinity of
bacteria are to be regarded partly as the _direct result_ of the action of
toxins on living cells, and partly as indicating a _reaction_ on the part
of the tissues. (Many such changes are usually grouped together under the
heading of "inflammation" of varying degree--acute, subacute and chronic.)
Degeneration and death of cells, haemorrhages, serous and fibrinous
exudations, leucocyte emigration, proliferation of connective tissue and
other cells, may be mentioned as some of the fundamental changes. Acute
inflammation of various types, suppuration, granulation-tissue formation,
&c., represent some of the complex resulting processes. The changes
produced at a distance by distribution of toxins may be very
manifold--cloudy swelling and fatty degeneration, serous effusions,
capillary haemorrhages, various degenerations of muscle, hyaline
degeneration of small blood-vessels, and, in certain chronic diseases, waxy
degeneration, all of which may be widespread, are examples of the effects
of toxins, rapid or slow in action. Again, in certain cases the toxin has a
special affinity for certain tissues. Thus in diphtheria changes in both
nerve cells and nerve fibres have been found, and in tetanus minute
alterations in the nucleus and protoplasm of nerve cells.

[Sidenote: Symptoms.]

The lesions mentioned are in many instances necessarily accompanied by
functional disturbances or clinical symptoms, varying according to site,
and to the nature and degree of the affection. In addition, however, there
occur in bacterial diseases symptoms to which the correlated structural
changes have not yet been demonstrated. Amongst these the most important is
f