78 PATHOGENIC BACTERIA.

blood in relation to its leucocytes, found that when a
marked experimental hypoleucocytosis was produced, the
bactericidal power of the blood was markedly diminished.
The most interesting feature of his work was the discov-
ery that bactericidal matter could be extracted from
crushed leucocytes, and that it could be subjected to a
temperature of 60° C. without change, thus differing
markedly from the alexins.

Much discussion has arisen as to exactly what the pro-
tective substances are. Buchner has applied the term
alcxin to the protective proteid substances found in the
blood of naturally immune animals. Hankin has given
us, together with an extension of Buchner's idea, a con-
siderable nomenclature of somewhat questionable utility.
He divides the protective substances (alexins) into sosins,
which occur in the blood of animals with natural immu-
nity, andphylaxins^ which occur in the blood of animals
with acquired immunity. Both sozins and phylaxins are
divisible into two groups—thus: a sozin which acts de-
structively upon bacteria is called a myco-sosin ; one
which neutralizes bacterial poisons, a toxo-sosin. A pin-
laxin which acts destructively upon bacteria is called a
myco-phylaxiii; one which neutralizes bacterial toxins,
a toxo-pkylaxiu.

The anti-microbic serums obtained by Pfeiffer, Kolle,
Loffler, and Abel from dogs and other animals immunized
to typhoid fever belong in the group of myco-phylaxins.
The toxo-phylaxins are the antitoxins.

5. THE THEORY OF ANTITOXINS.—It is a well-known
fact that individuals can accustom themselves to the use
of certain poisons, as tobacco, opium, and arsenic, so as
to experience no inconvenience from what would be poi-
sonous doses for other individuals. This is purely a
matter of tolerance, but is of interest in connection with
the observations which are to follow.

Ehrlich has shown that animals can tolerate Gradually
increasing doses of ricin and abrin, provided that up to
a certain point the increase of dosage is very small