Yiengst (Amer. Jour. Vet. Res., 3, 1942, 312) state that each organism undergoes growth which is then followed by multiple fission resulting in the formation of eight small spherical bodies. Studies on the life cycle of this organism in arthropods are limited. Regendanz (Zent. f. Bakt., I Abt., Orig., 137, 1933, 214) claims to have demon- strated granules varying from 0.1 to 0.4 microns in diameter in the salivary glands of known-infected Dermacentor andersoni and Dermacentor variabilis adult ticks. Cultivated on Bass medium. Continued to grow through two generations, but growth could not be detected after the third passage. No growth in a wide variety of bacteriological and tissue-culture media, in chick embryo or in sealed collodion bags containing infective blood which had been placed in the peritoneal cavity of a rabbit. Non-filterable with Berkefeld filter (du Toit, Rept. Direct. Vet. Educ. Res., Union So. Africa, Pt. I, 1928, 157). Filterable with a three-pound Mandler filter (Foot, No. Amer. Vet., 35, 1954, 19). Immunology: No authentic case of true natural immunity in cattle has been estab- lished. Calves under one year of age show a milder reaction than do older animals. Ac- quired immunity occurs in (1) the latently infected ox, (2) the infected ox after sple- nectomy and recovery from the disease, (3) the non-splenectomized, non-carrier ox fol- lowing infection, and (4) animals other than the ox following infection. Carrier state usually persists for periods longer than 12 years. Autosterilization in both non-sple- nectomized and splenectomized cattle is of relatively rare occurrence. A partial cross immunity exists between this organism and A. centrale. Serology: Complement fixation has been reported with sera of carrier cattle. About 90 per cent of the serum samples drawn from known carriers gave positive results while 10 per cent gave discordant reactions. Anti- bodies were detected in the sera of artifi- cially infected animals before the organism was microscopically demonstrable. Pathogenicity: Infected blood, washed red blood cells and organ suspensions pro- duce infection by the subcutaneous, intra- muscular and intravenous routes. Infectious for cattle, zebu, water buffalo {Babalus bab- alis), bison {Bison bison), African antelopes (white-tailed gnu {Connochaetes gnou), bles- buck (Damaliscus pygargus albifrons) and duiker (Sylvicapra grimmia)) , American deer (southern black-tailed deer and Rocky Mountain mule deer (Odocoileus spp.)), elk and camel (Camehis bactrianus). Sheep and goats develop a submicroscopic infection. The African buffalo {Syncerus caffer) is re- fractory. Rabbits, guinea pigs, white rats, gray rats, white mice, field mice, dogs, cats, ferrets and chickens are all refractory to bovine anaplasmosis. Mortality has been re- corded in cattle, zebu, water buffalo and camel. Antibiotic therapy: True sterilization of latent or recognized infection occurs with massive repeated doses of aureomycin and terramycin. Source: Observed by Theiler {op. cit., 1910, 7) in the blood of infected cattle. Habitat: Found in arthropods such as Argas persicus, Boophilus annulahis, B. aus- tralis, B. calcaratus, B. decoloratus, B. vii- crophis, Dermacentor albipictus, D. andersoni, D. occidentalus, D. variabilis, Haemaphysalis cinnabarina punctata, Hyalomma excavatum, Ixodes ricinus, I. scapularis, Rhipicephalus bursa, R. sanguineus and R. simus. Also found in the erythrocytes of susceptible animals. World wide distribution. 2. Anaplasma centrale Theiler, 1911. (1st Rept. Dir. Vet. Res., Union So. Africa, 1911, 7.) cen.tra'le. L. adj. centralis central. In blood smears fixed with May-Griinwald and stained with Giemsa, the organisms ap- pear in erythrocytes as irregularly spher- ical, chromatic granules which stain a deep purple color. Vary in diameter from 0.4 to 0.95, averaging 0.65, micron. Resembles A. marginale very closely but differs from it bj^ its slightly greater size and by its usually central position in the erythrocyte. Approx- imately 88 per cent of the organisms are situated at or near the center and 12 per cent at or near the margin of the host cell. Usually occurs singly in the red blood cells, but double forms are not uncommon. Rarely
