CHOLERA. 323 clothing, etc. are readily rendered harmless by the proper use of disinfectants. Water and foods are rendered in- nocuous by boiling or cooking. Vessels may be disin- fected by thorough washings with jets of boiling water .thrown upon them through hose. Baggage can be steril- ized by superheated steam. It often becomes a matter of importance to detect the presence of cholera in drinking-water, and, as the dilu- tion in which the bacteria exist in such a liquid may be very great, much difficulty is experienced in finding them by ordinary methods. One of the most expeditious meth- ods that have been recommended is that of L,6ffler, who adds 200 c. cm. of the water to be examined to 10 c. cm. of bouillon, allows the mixture to stand in an incubator for twelve to twenty-four hours, and then makes plate- cultures from the superficial layer of the liquid, where, if present, the development of the spirilla will be most rapid because of the presence of air. A similar method can be used to detect the spirilla when their presence is suspected in feces. Gruber and Wiener, Haffkine, Pawlowsky, and Pfeiffer have all succeeded in immunizing animals against the toxic substances removed from cholera cultures or against living cultures properly injected. There seems, accord- ing to the researches of Pfeiffer, to be no doubt that in the blood of the protected animals a protective substance is present. In the peritoneal infection of guinea-pigs the spirilla grow vigorously in the peritoneal cavity, and can be found in immense numbers after twelve to twenty- four hours. If, however, together with the culture used for inoculation, a few drops of the protective serum be in- troduced, Pfeiffer found that instead of multiplying the organisms underwent a peculiar granular degeneration and disappeared, the unprotected animal dying, the pro- tected animal remaining well. Pfeiffer and Vogedes1 have suggested the application -of this " immunity-reaction n for the positive differentia- 1 Centralbl.fur Bakt. imd Parasitenk., March 21, 1896, Bd. xix., No. II.