The occurrence of P. pitheci was recorded by Ross (1905) in several monkeys belonging to the genus Cercopithecus. The affected animals did not show any clinical symptoms apart from febrile reactions. Three years later the same preparations were re-examined by Nuttall
and Graham-Smith, who stated that these parasites were of the P. bigeminum and P. canis type. Castellani and Chalmers (1908) described piroplasms in a monkey Mlacacus pileatus under the name
P. cellii. A detailed account on the pathogenicity of P. pitheci in
splenectomized and non-splenectomized monkeys belonging to the genus
Cercopithecus and:Macacus is given by Kikuth (1927). His experiments showed that non-splenectomized monkeys did not suffer from the iufec:tion, whereas in splenectomized animals numerous parasites appeared which produced severe anaemia, loss in condition and in one
case death. Furthermore, he was able to show that trypan blue caused the parasites to disappear from the peripheral blood. Schwetz (1933) described piroplasms resembling those described
by Ross in two monkeys, one belonging to the genus Cercopithecus
and the other to a species of Cercocoebus. Through the kindness of Dr. A. D. Thomas of this Institute the ·writer obtained blood and spleen smears from an apparently healthy vervet-monkey which was shot on the farm Rossbach in the district Zoutpansberg in the Transvaal.