ards their
conditions of precipitation and relative instability, and the fact that in
most cases a considerable period intervenes between the time of injection
and the occurrence of symptoms has been adduced in support of the view that
enzymes are present. In the case of diphtheria Sidney Martin obtained toxic
albumoses in the spleen, which he considered were due to the digestive
action of an enzyme formed by the bacillus in the membrane and absorbed
into the circulation. According to this view, then, a part at least of the
directly toxic substance is produced in the living body by enzymes present
in the so-called toxin obtained from the bacterial culture. Recent
researches go to show that enzymes play a greater part in fermentation by
living ferments than was formerly supposed, and by analogy it is likely
that they are also concerned in the processes of disease. But this has not
been proved, and hitherto no enzyme has been separated from a pathogenic
bacterium capable of forming, by digestive or other action, the toxic
bodies from proteids outside the body. It is also to be noted that, as in
the case of poisons of known constitution, each toxin has a minimum lethal
dose which is proportionate to the weight of the animal and which can be
ascertained with a fair degree of accuracy.

The action of toxins is little understood. It consists in all probability
of disturbance, by means of the chemical affinities of the toxin, of the
highly complicated molecules of living cells. This disturbance results in
disintegration to a varying degree, and may produce changes visible on
microscopic examination. In other cases such changes cannot be detected,
and the only evidence of their occurrence may be the associated symptoms.
The very important work of Ehrlich on diphtheria toxin shows that in the
molecule of toxin there are at least two chief atom groups--one, the
"haptophorous," by which the toxin molecule is attached to the cell
protoplasm; and the other the "toxophorous," which has a ferment-like
action on the living molecule, producing a disturbance which results in the
toxic symptoms. On this theory, susceptibility to a toxin will imply both a
chemical affinity of certain tissues for the toxin molecule and also
sensitiveness to its actions, and, furthermore, non-susceptibility may
result from the absence of either of these two properties.

[Sidenote: Bacterial infection.]

A bacterial infection when analysed is seen to be of t