About the same time attention was devoted to the disease of West African negroes known for a century as “sleeping sickness.” Castellani (1903) was the first to succeed in demonstrating the presence of trypanosomes (at first called _T. ugandense_) in centrifugalized cerebro-spinal fluid obtained by puncture from cases of sleeping sickness in Uganda. Similar discoveries were made by Bruce, who also found trypanosomes in the blood of those attacked with sleeping sickness. Sambon regarded a species of _Glossina_ as the transmitter. From consideration of the geographical distribution of the disease Christy regarded _Glossina palpalis_ as the transmitter. Brumpt first thought it was _G. morsitans_, but, later, supported the view of _G. palpalis_. Bruce, Nabarro and Greig also named the same insect as the transmitter, not only for geographical reasons but also because healthy apes became infected by the bite of certain _G. palpalis_. The inoculation of cerebro-spinal fluid from subjects of sleeping sickness into the spinal canal of apes (_Macacus_) had the same result. Just as the discovery of the malarial parasites called forth a whole flood of research memoirs which were followed by a second series on the relation of the mosquitoes to malaria, so a similar outpouring occurred after the discovery of the pathogenic trypanosomes of mammals and men. In both cases the inquiry was not limited to the stages in man and other vertebrate hosts, but the fate of the parasites in the intermediate (invertebrate) hosts was investigated, and allied species were obtained from many different hosts. Novy and MacNeal (1903) were the first to cultivate trypanosomes in artificial media (blood-agar). In 1910 Stephens and Fantham recorded the presence of another human trypanosome, _T. rhodesiense_, from a case of sleeping sickness in Rhodesia, where _G. palpalis_ was absent. Kinghorn has since demonstrated that _T. rhodesiense_ is transmitted by _G. morsitans_. Kinghorn and Yorke believe that big game (_e.g._, antelope) is the reservoir of _T. rhodesiense_. The output of literature on trypanosomiasis in men and animals is enormous. To cope with it the Sleeping _Sickness Bureau Bulletin_ was founded in 1908, and it is now (since November 1912) continued as a section of the _Tropical Diseases Bulletin_, wherein current literature is reviewed. GENERAL. Trypanosomes occur in the blood of representatives of all the vertebrate classes. Often the trypanosomes occur so scantily in the blood that they are overlooked on examination. A useful aid in detecting the flagellates in such cases consists in the use of cultures of the blood of the host on artificial media. Stimulated by the medium multiplication occurs, and hence the parasites are more easily detected. [For the composition of such culture media see Appendix.]