GENUS: TRYPANOSOMA 443 



parts in the act of feeding, or indirectly by the vertebrate accidentally 

 ingesting the infective fseces. The vast majority of trypanosomes are 

 known only as they occur in the blood of the vertebrate, but it is safe to 

 assume that an invertebrate host exists for every one, with the possible 

 exception of Trypanosoma equijjerdum, the cause of dourine, which is 

 handed on directly from horse to horse during the sexual act. In some 

 instances the trypanosome is only known in the invertebrate, but that a 

 vertebrate host also exists is rendered probable by the fact that typical 

 infections can be produced in laboratory animals by inoculating them 

 with these insect flagellates. Such infections differ from the transitory 

 infections which may result from the inoculation of purely insect lepto- 

 monas, crithidia, or herpetomonas, which, as explained above, cannot be 

 regarded as having vertebrate hosts. 



Trypanosomes have been found in every class of vertebrate, and it is 

 because some of them produce disease in man and domestic animals that 

 these flagellates have attained considerable importance and have been 

 the subject of many investigations, the literature dealing with which is 

 now very extensive. 



According to Laveran and Mesnil, whose excellent treatise on trypano- 

 somes and trypanosomiasis summarizes our knowledge of these flagellates 

 up to the year 1912, the first observer to see a member of the genus was 

 Valentin of Berne, who discovered a trypanosome in the blood of the 

 trout, Salmofario, in 1841. In the two succeeding years Gluge of Brussels, 

 Mayer of Bonne, and Gruby of Paris published three papers on the try- 

 panosomes of the frog. To these organisms Gruby gave the name Try- 

 panosoma. From 1843 to 1880 little advance was made in our knowledge 

 of trypanosomes except for their discovery in various amphibia, the black 

 rat, the field mouse, and the mole. Timothy Lewis (1878, 1879) published 

 accounts of the trypanosome of the rat in India, but these flagellates were 

 first recognized as of great importance on the announcement in India of 

 the discovery of a trypanosome in the blood of horses and camels suffering 

 from surra by Griffith Evans (1880), and in the disease nagana of horses 

 and cattle in Africa by Bruce (1895). Discovery of various other trypano- 

 somes in domestic and other animals followed these observations, which 

 led up to the discovery in the blood of a man in the Gambia by Forde of 

 an organism which was recognized and described as a trypanosome 

 {T. gambiense) by Button (1902). The next observer to see a trypanosome 

 in man was Castellani, who (1903) announced his discovery of a trypano- 

 some in the cerebro-spinal fluid of a case of sleeping sickness in Uganda. 

 This observation was confirmed immediately afterwards by Bruce and 

 Nabarro (1903), who demonstrated the causal relationship between the 

 trypanosome and the disease. 



