At the end of my first cholera campaign, in August, 1895, there were altogether 31,056 natives of India, 125 Eurasians, 869 Europeans of the civil population, 6,627 native officers and sepoys, and 294 officers with 3,206 men of the British troops stationed in India, in all 41,787 people, who had submitted to inoculation. Observations instituted among them, especially among prisoners, soldiers and coolies in tea estates, with regard to whom detailed records could be kept, went to confirm the results as detailed above. In order to lengthen, if possible, the period of immunity, the plan was formed of inoculating stronger vaccines and in higher doses. The inoculations are now carried on in a Government laboratory, in Purulia, Bengal, chiefly among the people emigrating to the cholera districts of Assam, and there is no doubt that in the course of time a marked effect upon the prevalence of cholera in those districts will be produced and valuable theoretical data will be obtained. * * * * * There was one noticeable feature about the results of the inoculation against cholera which early attracted my attention, and this was that while the number of attacks and the absolute number of deaths was strikingly influenced by the operation, the proportion of deaths to those attacked did not appear to be changed. The case incidence was effectively checked, but the ‘case mortality’ was not reduced. The inoculation diminished the chances of an attack of cholera--that is, the chances of the cholera virus penetrating into the tissues of a man; but if it so happened that the patient was attacked and the virus found an entrance and started growing in the system notwithstanding the inoculation, the latter would not assist in mitigating the severity of the symptoms or reducing the fatality of the disease. In analyzing this result further, it seemed to me permissible to assume that the vaccine protected against the cholera microbes themselves, but did not protect against their poisonous products, which are the cause of the actual symptoms. This interpretation of the facts found support in a set of laboratory experiments by Professor Pfeiffer and Dr. Kolle, of Koch’s Institute, in Berlin, who showed that the blood serum of animals and persons inoculated with the cholera vaccine, as practiced in India, acquired an intense power of destroying cholera microbes, but exhibited no properties capable of counteracting the effect of their toxic products--no ‘antitoxic properties’. Combined with those of previous experimenters these results tended to prove that two kinds of immunity could be produced separately, and it became incumbent to devise a plan which would secure not only a lowering of susceptibility to the disease, but also a reduction in the case mortality.