The authors studied the effect of various excipients on Br. abortus strain 19 in vivo and in vitro. The excipients included normal saline, liquid paraffin, oil of sweet almonds, lanolin, saponin, and cholesterol, and certain mixtures of these. Tables are given showing (1) the viability of the organism at incubator, room, and refrigerator temperatures for periods up to seven weeks, (2) the reaction produced and the possibility of recovering Br. abortus from vaccinal sites in cows or yearling steers after periods up to five months, (3) the local reactions, agglutinin titres, and possibility of recovering the organism after various periods in inoculated rabbits, and (4) the virulence of strains obtained from vaccinated cows after various periods. Unexpected differences were found between the effects of various excipients in vitro and in vivo, e.g. whilst suspensions in 50% lanolin in liquid paraffin were sterile within 96 hours at 37.5°C. in vitro, viable brucella were isolated from vaccinal sites 85 days after inoculation of identical suspensions. Pronounced differences were found in vitro at incubator temperatures, similar effects of less degree being noted at lower temperatures. Lanolin and liquid paraffin mixtures produced rapid sterilization at all temperatures, the rate appearing to run parallel with the percentage of lanolin present. Oil of sweet almonds containing cholesterol showed a similar action but of less degree, seven days at 37°C. being necessary before sterilization was complete. Viability was maintained for longer periods in oil of sweet almonds alone (14 days), liquid paraffin containing cholesterol (4-5 weeks), liquid paraffin alone (six weeks), and 1 or 2% saponin or saline (over seven weeks). For the experiments in cows (14 in number) the same numbers of organisms were injected in various volumes of excipient at four different sites and material was aspirated with a syringe after various periods, or a small biopsy made. In general a rise of about 3°F. in body temperature with subsidence within tarée days was observed irrespective of the excipient used. Differences were found in the persistence of local reactions, but not in their initial intensity, which usually reached its maximum in 4-6 days. Lesions from vaccines in saline were resorbed within about 14 days; résorption of those from 4 or 6 cholesterol in liquid paraffin took about 65 days, and of those from 50% lanolin in the same vehicle over five months. Recovery of viable organisms from the vaccinai sites showed some irregularity, but outstanding findings were the rapid disappearance in the case of liquid paraffin or oil of sweet almonds alone, the long period of viability in the case of saline (up to 65 days) and lanolin-paraffin mixtures (up to 65 and 73 days) and the period of 8-5 months for cholesterol-paraffin mixtures, large numbers being recovered in two out of three cases for periods up to nearly three months. For the experiments on heifers (13 in ail) only three vehicles were used, viz, saline, 1% saponin, and 2% cholesterol in liquid paraffin. Results were similar to those given above for cows. Frequent agglutination tests made on these animals showed no significant difference in the average titre produced by the three vaccines. The same vaccines were used for rabbits and the results obtained again showed marked localization and persistence of lesions from the 2 % cholesterol-paraffin mixture. BRUcella were recovered up to 44 days in the case of saline and 1 saponin vaccine and in large numbers for more than 55 days (the longest period recorded) in the case of 2% cholesterol-paraffin. Two rabbits given saponin and cholesterol vaccines respectively showed a much more persistent agglutinin response than one given a saline vaccine. Virulence tests made in g. pigs with strains recovered from ten cows after periods varying from 59-97 days showed no enhancement of virulence. On the basis that retarded antigen absorption may induce increased immuno-logical response, it is suggested that 2% cholesterol in liquid paraffin, which caused circumscribed and persistent local reactions from which brucella could be cultivated for over five months, deserves further study as an excipient for brucella vaccines.-A. W. S.