The immunisation of the rabbit against the Diplococcus pneumoniæ may be instanced as an example of the general methods of immunisation of laboratory animals. 1. Take a full grown rabbit weighing not less than 1200 to 1500 grammes (large rabbits of 2000 grammes and over are the most suitable for immunising experiments). Observe weight and temperature carefully during the few days occupied in the following steps. 2. Inoculate a small rabbit intraperitoneally with one or two loopfuls of a twenty-four-hour-old blood agar cultivation of a _virulent_ strain of Diplococcus pneumoniæ. Death should follow within twenty-four hours, and in any case will not be delayed beyond forty-eight hours. 3. Under aseptic precautions, at the post-mortem, transfer a loopful of heart blood to an Erlenmeyer flask containing 50 c.c. sterile nutrient broth. Incubate at 37° C. for twenty-four hours. 4. Prepare also several blood agar cultures from the heart blood of the rabbit, label them all O.C. (original culture). After twenty-four hours incubation at 37° C. place an india-rubber cap over the plugged mouth of the tube of all but one of these cultures and paint the cap with Canada balsam or shellac varnish, dry, and replace in the hot incubator. This will prevent evaporation, and cultures thus sealed will remain unaltered in virulence for a considerable time. 5. Make a fresh subcultivation on blood agar from the uncapped O.C. cultivation and after twenty-four hours incubation at 37° C. determine the minimal lethal dose of this strain upon a series of mice (see page 316). 6. Suspend the flask containing the twenty-four-hour-old broth culture (step 3) in the water-bath at 60° C. for one hour. Cool the flask rapidly under a stream of cold water. 7. Determine the sterility of this (?) killed cultivation by transferring one cubic centimetre to each of several tubes of nutrient broth, and incubate at 37° C. for twenty-four hours. If growth of Diplococcus pneumoniæ occurs, again heat culture in water-bath at 60° C. for one hour and again test for sterility. 8. Inject the selected rabbit intravenously (see page 363) with 2 c.c. of the killed cultivation, and inject a further 10 c.c. into the peritoneal cavity. During the next few days the animal will lose some weight and perhaps show a certain amount of pyrexia. 9. When the temperature and weight have again returned to normal--generally about seven days after the inoculation--again inject killed cultivation, this time giving a dose of 5 c.c. intravenously and 20 c.c. intraperitoneally. A temperature and weight reaction similar to, but less marked than that following the first injection will probably be observed, but after about a week's interval the animal will be ready for the next injection.