In the human subject, multiplication in the blood-stream does not occur
to any great extent. In some general acute pyogenic infections, such as
osteomyelitis, cellulitis, etc., pure cultures of staphylococci or of
streptococci may be obtained from the blood. In pneumococcal and typhoid
infections, also, the organisms may be found in the blood.
It is by the vital changes they bring about in the parts where they
settle that micro-organisms disturb the health of the patient. In
deriving nourishment from the complex organic compounds in which they
nourish, the organisms evolve, probably by means of a ferment, certain
chemical products of unknown composition, but probably colloidal in
nature, and known as _toxins_. When these poisons are absorbed into the
general circulation they give rise to certain groups of symptoms--such
as rise of temperature, associated circulatory and respiratory
derangements, interference with the gastro-intestinal functions and also
with those of the nervous system--which go to make up the condition
known as blood-poisoning, toxaemia, or _bacterial intoxication_. In
addition to this, certain bacteria produce toxins that give rise to
definite and distinct groups of symptoms--such as the convulsions of
tetanus, or the paralyses that follow diphtheria.
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