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XXVIII] fever, transient œdema and tenderness at the seat of injection, the first evidence of constitutional disturbance appearing from two to three hours after the injection is made. The fever and general indisposition last from twenty-four to thirty-six hours, the local symptoms gradually disappearing in from three to four days. The symptoms following the second injection— made from three to four days after the first— are generally more marked, but of shprter duration. The microbes injected die; it is the substances set free on their death which confer the immunity. It is found that carbolized cultures— that is, dead vibrios— produce the same immunizing and constitutional effects, though in a somewhat milder and probably less permanent degree. How long the immunity conferred by these injections endures has not been definitely settled.*

In consequence of an experiment on himself, Haffkine found that, although the virulent comma bacillus produced necrotic effects at the site of inoculation in guineapigs, it did not do so in man. Accordingly, he has abandoned his original method of a primary inoculation with an attenuated virus, and has since countenanced immediate inoculation with virulent, recently-isolated vibrios, without further preparation. According to Powell, the method is as follows:—

" The whole surface of agar in a sloped tube is inoculated with the comma and cultivated for twenty-four to thirty-six hours at a temperature of 40° C. The whole surface should then be covered with a uniform layer of growth. Sterilized water is then added to one-third the height of the agar, and the growth washed off and suspended in the water by rapidly rotating or shaking, till the surface of the agar is quite clear. Half a cubic centimetre, about nine minims, is the dose for an average adult."

Powell's results are highly favourable— namely, 198 cases of cholera with 124 deaths among 6,549 non-inoculated tea-garden coolies in Assam, against 27 cases and 14 deaths among 5,778 inoculated coolies.