PA THOGENIC BACTERIA.

tion of cholera spirilla in cultures. A hanging-drop of
a i : 50 mixture of powerful anti-cholera serum and a
particle of cholera culture is made and examined under
the microscope. The cholera spirilla at once become in-
active, and are in a short time converted into little rolled-
up masses. If the culture added be a spirillum other
than the true spirillum of cholera, instead of destruc-
tion of the micro-organisms following exposure to the
serum, they multiply and thrive in the mixture of serum
and bouillon.

The specific immunity-reaction of the cholera serum
has been carefully studied by I^oburnheim,1 and is
specific against cholera alone. The protection is not
due to the strongly bactericidal property of the serum,
but to its stimulating effect upon the body-cells. If
the serum be heated to 6o°~7O° C., and its bactericidal
power thus destroyed, it is still capable of producing
immunity.

The immunity produced by the injection of the spirilla
into guinea-pigs continues in some cases as long as four
and a half months, but the power of the serum to con-
fer immunity is lost much sooner.

Of the numerous attempts which have from time to
time been made, and are still being made, to produce
immunity against cholera in man or to cure cholera
when once established in the hurrian organism, nothing
very favorable can at the present time be said. Experi-
ments in this field are not new: we find Dr. Ferran ad-
ministering hypodermic injections of pure virulent cul-
tures of the cholera spirillum in Spain as early as 1885,
in the hope of bringing about immunity. The more mod-
ern work of Haffkine seems to be followed by a distinct
diminution of mortality in protected individuals. Ac-
cording to the work of this investigator, two vaccines are
used, one of which, being mild, prepares the animal (or
man) for a powerful vaccine, which, were it not preceded
by the weaker form, would bring about extensive tissue-

1 Zeitschrift fur Hygiene-, xx., p. 438.