•conditions their vitality, when dried on paper, silk, etc.,
continues for a few days. In air that is moist the dura-
tion of vitality is prolonged to about a week. In sand
exposed to a dry atmosphere they die in five days in the
light; in sixteen to eighteen days in the dark. When
the sand is exposed to a moist atmosphere the duration
of vitality is doubled. In fine earth they remained alive
seventy-five to one hundred and five days in dry air, and
•one hundred and twenty days in moist air.
From time to time reference has been made to the
toxin elaborated by the diphtheria bacillus. Roux and
Yersiii first demonstrated the existence of this substance
in cultures passed through a Pasteur porcelain filter.
The toxin is intensely poisonous; it is not an albumin-
ous substance, and can be elaborated by the bacilli
when grown in non-albuminous urine, or, as suggested
by Uschinsky, in non-albuminous solutions whose prin-
cipal ingredient is asparagin. The toxic value of the
cultures is greatest in the second or third week.
In addition to the toxin, a toxalbumin has been isolated
by Brieger and Frankel.
Behring discovered that the blood of animals rendered
immune to diphtheria by inoculation, first with attenu-
ated and then with virulent organisms, contained a neu-
tralizing substance which was capable of annulling the
effects of the bacilli or the toxin when simultaneously or
subsequently inoculated into non-protected animals. This
substance, in solution in the blood-serum of the immu-
nized animals, is the diphtheria antitoxin.
The preparation of the antitoxin for therapeutic pur-
poses received a further elaboration in the hands of Roux.
The subject is one of great interest, but must be consid-
ered briefly in a work of this kind.
The antitoxin is manufactured commercially at present,
the method being the immunization of large animals to
great quantities of the toxin, and the withdrawal of their
antitoxic blood when the proper degree of immunity has
been attained. The details are as follows: