14 NATURAL HISTORY OF SLEEPING SICKNESS 



now known that in nearly every place rats are infected 

 with this species, often to the extent of 50 per cent., but 

 it is not harmful to them unless present in great numbers. 

 The first disease-producing Trypanosome described was 

 T. evansi, which kills numbers of horses, camels, elephants 

 and dogs in Asia and North Africa by causing a disease 

 known as " Surra " ; it was discovered in 1880. Not 

 until 1895 was the next pathogenic species discovered, 

 and this was an extremely important one, the know- 

 ledge of which was of the utmost help to the subsequent 

 investigations into Sleeping Sickness. 



This species was named T. brucei, after Sir David 

 Bruce, who proved it to be the cause of " Tse-tse fly 

 disease " or " Nagana " in South Africa.^ 



In 1901 another species was described as T. equiperdum, 

 the cause of " Dourine " in stallions, brood mares, and 

 donkeys in America and North Africa. Also in 1901 

 was discovered T. gambiense, the first Trypanosome to 

 be known for a cause of disease in man.^ 



In 1902 T. equinum was shown to be the cause of *' Mai 

 de Caderas," a fatal disease of horses in Brazil and the 

 Argentine Republic. Another human Trypanosome was 

 discovered in 1909,' by Chagas ; it causes in children, 

 and adults who have not become immune in childhood, 

 chronic fever, enlargement of the thyroid gland, and 

 puffiness of the face, and may rarely result in death. 

 This species was found to differ sufficiently in its life- 

 history to be put in a new genus, and has been named 

 Schizotrypanum cruzi. In 1910 it was shown that the 

 cause of the acute Trypanosomiasis of Rhodesia was 

 differentiated, not by its morphology, but by its effects 



^ Preliminary Report on the Tse-tse fly disease or Nagana in Zulu- 

 land, 1895. 



* British Medical Journal, 1902, January 4th, p. 42. 



8 Chagas, Brazil Medico, 1909, April 22nd. See Bull. Inst. Pasteur, 

 1909, May 30th, pp. 453-4. Also Bulletin of the Sleeping Sickness 

 Bureau, vol. 1, p. 252; vol. 2, p. 117. 



