THE SLEEPING SICKNESS 175 



A little later, namely, in the year 1895, came Bruce's 

 discovery of a trypanosome associated with a tsetze fly 

 in the production of the terrible nagana disease of the 

 "fly-belts" of South Africa, which renders whole terri- 

 tories impassable for horses or cattle (fig. 466). The 

 remarkable and important observation was made by Bruce 

 that this trypanosome (known as T. Brucei} inhabits 

 the blood of big game without injuring them, just as 

 the rat's trypanosome inhabits the rat's blood without 

 producing disease ; and that it is only when the try- 

 panosome is carried from these natural wild " hosts " to 

 domesticated animals introduced by man, such as horses 

 asses, cattle, and dogs, that disease results. The wild 

 animals are " immune " to Bruce's trypanosome ; the 

 introduced animals are poisoned by the products of its 

 growth and fissile multiplication in their blood. 



Since Bruce's researches on nagana, a trypanosome, 

 T. equinum (fig. 4&D), has been discovered in the horse- 

 ranches of South America, where it causes deadly disease, 

 the mat de caderas, among the collected horses ; and a 

 curiously large-sized trypanosome has been found by 

 Theiler in the blood of cattle in the Transvaal. Down 

 to a recent date no trypanosome had been found in 

 the blood of man ; and indeed it is almost certain that 

 none of the kinds hitherto mentioned can survive in his 

 blood. But in 1902 Button discovered a trypanosome 

 in the blood of a West African patient ; and a few 

 other cases were noted. This trypanosome of human 

 blood was called by Button T. Gambiense. It was not 

 found to be connected with any serious symptoms, a 

 little fever being the only disturbance noted. It now, 

 however, appears that this trypanosome in the blood 

 is the preliminary stage of the infection which ends in 

 sleeping sickness ; and, as we have seen, in a population 



