three or four organisms may be seen in the same red blood cell. During the height of the reaction, as many as 15 per cent or more of the erj^throcj'tes may be parasitized. Re- sponsible for anemia and icterus. When ane- mic changes progress, the number of in- fected erythrocj-tes decreases to a point where they cannot be demonstrated micro- scopically. Recovery is usually followed by the reappearance of the organisms in rela- tively small numbers for a period of from 10 to 30 days and sometimes even longer. The life cycle of A. centrale is in all proba- bility the same as that of A. marginale. No attempts have yet been made to study the life cycle of A. centrale in the arthropod vector. Cultivation: No attempts have been made . Filterability: No information available. Immunology: No authentic case of true natural immunity in cattle has been estab- lished. Acquired immunity occurs in (1) the latently infected ox, (2) the infected ox after splenectomy and recovery from dis- ease, the period of resistance corresponding to the duration of latency, (3) the non- splenectomized, non-carrier ox following in- fection, and (4) animals other than the ox following infection. Recovered animals re- main carriers for periods of up to 20 years. A partial cross immunity exists between this organism and A. marginale. A. centrale has been emploj^ed on the African continent and in Palestine as an immunizing agent against A. marginale. Approximatel}- 350,000 doses of A. centrale vaccine (infective cit- rated blood) are issued annually to farmers in South Africa. No cases of autosteriliza- tion have been observed. Serology: No work attempted. Pathogenicity: Infected blood and organ suspensions produce infection by the sub- cutaneous, intramuscular and intravenous roiites. A. centrale is infectious for cattle. The African antelope, the blesbuck (Dama- liscus pygargus albifrons), develops a sub- microscopic infection. Antibiotic therapy: No information avail- able. Aureomycin and terramycin may pos- sibh' be as effective for .4. centrale as for ^4. marginale. Source: Observed in the blood of infected cattle. Habitat: Found in the arthropods Bo- ophilus decoloratus and Haemaphysalis cin- naharina punctata; also found in the erythro- cytes of cattle. Found in Africa, Roumania and Palestine. 3. Anaplasma ovis Lestoquard, 1924. (Bull. Soc. path, exot., 17, 1924, 784.) o'vis. L. noun ovis the sheep. In blood smears fixed with May-Griin- wald and stained with Giemsa, the organ- isms appear in the red blood cells as irregu- larly spherical, chromatic granules which stain a deep purple color. Vary from 0.4 to 0.8, averaging 0.5, micron in diameter. Re- sembles A . marginale very closelj- but differs from the latter by its pathogenicity and by its position in the erythrocytes. Approxi- mately 65 per cent of the organisms are sit- uated at or near the margin and 35 per cent at or near the center of the erythrocyte. Occurs singly in the red blood cells, but double forms are not uncommon. Rarely three or four organisms may be seen in the same cell. During the height of the reaction, as many as 5 per cent or more of the eryth- rocj^tes may be parasitized. Responsible for anemia and icterus. When anemic changes progress, the nvmiber of infected erythro- cytes decreases to a point where they cannot be demonstrated microscopically. Recovery is usuallj' followed by the reappearance of the organisms in relatively small numbers for a period from 10 to 30 days and some- times even longer. The life cycle is in all probability the same as that of A. marginale. No attempts have j^et been made to studj' the life cycle of this organism in the arthro- pod vector. Cultivation: No attempts have yet been made. Filterability: No information available. Immunology: No authentic case of true natural immunity in sheep or goats has been established. Acquired immunity occurs in (1) latently infected sheep and goats, (2) the infected sheep and goat after splenec- tomy and recoverjr from the disease, the period of resistance corresponding to the duration of latency, (3) the non-splenecto-
