The spirillum of cholera has but little resistance to disinfecting agents or to drying. It is also rapidly overgrown by putrefactive bacteria and tends to disappear from sewage-contaminated water in a short time. In stools the vibrio dies in about one or two days in summer and in about a week in winter. The inoculation of animals by cholera cultures tends to produce an immune serum which is remarkable for its high agglutinating power, the titre at times going as high as 1 to 20,000. For agglutination tests in proving spirilla isolated from stools to be true cholera ones we use a serum of at least 1 to 4000 for its specific vibrio. Such a serum should agglutinate any true cholera spirillum in a 1 to 500 or 1 to 1000 dilution. The occurrence of bacteriolysis, when a small loopful of the culture emulsified in 1 cc. of 1 to 1000 dilution of the immune serum and then introduced into the peritoneal cavity of a guinea pig, is the surest proof that a suspected organism is that of cholera. This is shown when, upon removing a drop of the peritoneal fluid fifteen to twenty minutes afterward, there is noted an absence of motility and disintegration of the spirilla (_Pfeiffer’s phenomenon_). Complement fixation tests, using the rice-water stools or peptone solution cultures as antigen, are of less value than those above noted. Agglutination is the practical test and is almost as specific as that for bacteriolysis. =Epidemiology.=—Until recently our attention as to the methods of transmission of cholera was directed almost exclusively to the water and food supply, with a certain degree of consideration of danger from fomites, especially to that connected with clothing soiled by cholera discharges, it having been noted that those who wash such clothing showed a high incidence of infection. Later on the importance of flies in the spread of the disease was strongly insisted upon. At the present time we consider the cholera carrier the most important factor in cholera epidemiology and it is to the detection and isolation of such persons that we now chiefly direct our attention in the keeping out of a country of this dread disease. It will be remembered that Pettenkofer and Emmerich insisted upon the factors of soil and ground water in the spread of cholera. Emmerich now admits that the spirilla excreted by carriers can produce cholera but that such transference never gives origin to epidemics. For this to take place he thinks that the vibrios excreted by a carrier must come in contact with a soil which has been impregnated with a suitable medium drawn to the surface from the deeper layers of the soil by capillary suction. In such medium the vibrios flourish and acquire the property of actively producing nitrites from nitrates.