These vaccines are of the “killed bacteria” type of vaccines, and credit for their application to human disease belongs to Sir Almroth Wright (1896). The preparation of bacterial vaccines is very simple. Bacteria which are known to cause a certain disease are isolated in pure culture, grown on artificial media, killed either by chemicals or heat, standardized either by counting, or drying and weighing, and suspended in salt solution for subcutaneous injection. Salt suspension vaccines are usually given in three or four increasing doses, about one week apart. Le Moignic and Pinoy (58) first elaborated a lipovaccine for triple typhoid vaccination, which was used extensively in France during the war. Whitmore, Fennel and Peterson have recently also advised the drying of killed bacteria and the suspension of them in oil. This method makes it possible to give a single massive dose of bacteria which is sufficiently large to completely immunize the individual against the disease, and which prolongs the immunizing period by allowing slow absorption over a period of several weeks. These vaccines are called lipovaccines, have been adopted in the United States Army as the standard typhoid vaccine, and promise in time to supersede the salt suspensions entirely from a commercial standpoint. Many other modifications in the preparation of bacterial vaccines have been advised, notably the class known as sensitized vaccines. These are prepared by incubating bacterial vaccines for a time with the serum taken from animals already immunized against them. The serum apparently absorbs many of the toxic substances, and permits the injection of more efficient doses. Besredka advised the use of living cultures which had been incubated with immune sera, on the basis that vaccines so prepared were very active and non-toxic. The sensitizing treatment, however, does not stop the growing powers of the bacteria, and vaccines of the Besredka type are generally considered dangerous and so are little used. Sensitized killed bacterial vaccines, on the other hand, are quite popular.