to
antagonize 100 times the minimum lethal dose of a particular toxin to a
guinea-pig of 250 grm. weight, the indication that the toxin has been
antagonized being that a fatal result does not follow within five days
after the injection. In the case of diphtheria the antitoxic power of the
serum may reach 800 units per cubic centimetre, or even more. The laws of
antitoxin production and action are not confined to bacterial toxins, but
apply also to other vegetable and animal toxins, resembling them in
constitution, viz. the vegetable toxalbumoses and the snake-venom group
referred to above.

[Sidenote: Action of antitoxin.]

The production of antitoxin is one of the most striking facts of biological
science, and two important questions with regard to it must next be
considered, viz. how does the antitoxin act? and how is it formed within
the body? Theoretically there are two possible modes of action: antitoxin
may act by means of the cells of the body, _i.e._ indirectly or
physiologically; or it may act directly on the toxin, _i.e._ chemically or
physically. The second view may now be said to be established, and, though
the question cannot be fully discussed here, the chief grounds in support
of a direct action may be given. (a) The action of antitoxin on toxin, as
tested by neutralization effects, takes place more quickly in concentrated
than in weak solutions, and more quickly at a warm (within certain limits)
than at a cold temperature. (b) Antitoxin acts more powerfully when
injected along with the toxin than when injected at the same time in
another part of the body; if its action were on the tissue-cells one would
expect that the site of injection would be immaterial. For example, the
amount necessary to neutralize five times the lethal dose being determined,
twenty times that amount will neutralize a hundred times the lethal dose.
In the case of physiological antagonism of drugs this relationship does not
hold. (c) It has been shown by C. J. Martin and Cherry, and by A. A.
Kanthack and Cobbett, that in certain instances the toxin can be made to
pass through a gelatine membrane, whereas the antitoxin cannot, its
molecules being of larger size. If, however, toxin be mixed with antitoxin
for some time, it can no longer be passed through, presumably because it
has become combined with the antitoxin.

Lastly it may be mentioned that when a toxin has some action which can be
demonstrated in a test-tube experiment, fo