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.