196 THE HAEMOFLAGELLATES 



knowledge of which has in many cases thrown light upon the 

 etiology of maladies previously obscure. Thus, two characteristic 

 diseases, Dourine, which afflicts horses and mules in Northern 

 Africa and the Mediterranean littoral, and Mai de Caderas of 

 horses in South America, were next shown to be caused by 

 different Trypanosom.es ; and since then many other varieties of 

 trypanosomosis have been described, chiefly from Africa, the home 

 of the dreaded Tsetse-fly. 



Prominent among them, unfortunately, is human trypanosomosis. 

 The credit for first recognising a Trypanosome in human blood, 

 and describing it as such, must undoubtedly be assigned to Nepveu 

 (1898). The parasites were not definitely associated with disease, 

 however, till 1901, when they were seen in the blood of a European 

 in Senegambia suffering from intermittent fever. Forde first found 

 the organisms, but was uncertain of their nature ; he showed them 

 to Button, who recognised them as Trypanosomes, and gave this 

 form the name of Trypanosoma gambiense. A year later (1902) 

 Castellani discovered what has been shown to be the same parasite in 

 the cerebro-spinal fluid of patients suffering from sleeping-sickness 

 in Uganda, and it has since been conclusively proved by Bruce 

 and Nabarro that this organism is the true cause of that terrible 

 disease. 



More important, however, from the standpoint of Protozoology r 

 than these interesting medical discoveries have been the investigations 

 by Brumpt, Laveran and Mesnil, Leger, Minchin, Schaudinn, the 

 Sergents, and others during the last few years upon numerous other, 

 mostly " tolerated " forms ; to their researches, indeed, we owe most 

 of our knowledge at the present time, relating to the life-cycle of 

 the Haemoflagellates. And it is fitting, here, to pay a tribute to 

 the value of the characteristic stain first made known by Roman- 

 owsky, and its subsequent modifications (e.g. those of Giemsa, 

 Laveran, Leishman, etc.), without which, it is safe to say, this 

 progress would have been impossible. 



2. OCCURRENCE AND TRANSMISSION ; HABITAT AND EFFECTS 



ON HOST. 



(a) Occurrence and Transmission. 



Trypanosomes are harboured by members of all the chief classes 

 of Vertebrates, with the exception of Cyclostomes. Mammals, birds, 

 and fishes furnish, however, by far the greater number of hosts. Fewer 

 parasites have been described from Amphibia, and up till now only 

 from frogs ; while, among Reptiles, their occurrence has only been 

 observed in two or three instances. Data with regard to the 

 frequency with which individual species are to be met with, in any 



