DIPHTHERIA. 299

guinea-pig in three days). This period of time covered
that.of the greatest growth of the bacilli, as shown both
by the appearance of the culture and by the number of
colonies developing on agar plates."

"The bodies of the diphtheria bacilli did not at any
time contain toxin in considerable amounts." "The
type of growth of the bacilli and the rapidity and extent
of the production of toxin depended more on the reaction
of the bouillon than upon any other single factor."
" The best results were obtained in bouillon which, after
being neutralized to litmus, had about 7 c.cm. of normal
soda solution added to each liter. An excessive amount
of either acid or alkali prevented the development of
toxin." " Strong toxin was produced in bouillon con-
taining peptone ranging from i to 10 per cent." "The
strength of toxin averaged greater in the 2 and 4 per
cent peptone solution than in the I per cent."

"When the stage of acid reaction was brief and the
degree of acidity probably slight, strong toxin developed
while the culture bouillon was still acid; but when the
stage of acid reaction was prolonged little if any toxin
was produced until just before the fluid became alka-
line."

"Glucose is deleterious to the growth of the diphtheria
bacillus and to the production of toxin when it is present
in sufficient amounts to cause by its disintegration too
great a degree of acidity in the culture-fluid. When the
acid resulting from the decomposition of glucose is neu-
tralized by the addition of an alkali the diphtheria
bacillus again grows abundantly."

The Immunisation of the Animal.—The animals chosen
to furnish the antitoxic serum should be animals which
present a distinct natural immunity to ordinary doses of
the toxin, and should be sufficiently large to furnish large
quantities of the finished serum. Behring originally
employed dogs and sheep ; Aronson at first preferred the
goat; but Roux introduced the horse, which is more easi-
ly immunized than the other animals mentioned, and,