NAGANA OR TSE-TSE FLY DISEASE 555 



appeared incapable of acting as carriers of infection. Brace's 

 work as a whole pointed to the trypanosome as the cause of 

 nagana, and this has since been finally established by the 

 origination of the disease by artificial cultures of the organism. 



The Tr. Brucei (Fig. 168), according to Laveran, measures 

 in the horse from 28-33 /x long and from 1*5 to 2*5 /x broad ; in 

 the rat and dog it is somewhat shorter. It is motile, but its 

 activity is less than that of Tr. Lewisi. When stained it 

 presents the usual appearances ; its posterior end is usually 

 blunt, and the body often contains granules in the anterior 

 portion of its protoplasm. It divides longitudinally, and 

 according to Bradford and Plimmer a form of longitudinal 

 conjugation occurs in the blood. According to the same 

 observers, it can be kept alive for 5-6 days in blood outside 

 the body. It is less resistant to the action of cold than Tr. 

 Lewisi, perishing in a few days at 5-7 C., but like the other 

 organism it can withstand short exposures to temperatures down 

 to -191 C. ; it is quickly killed at 44-45 C. Novy and 

 MacNeal succeeded in cultivating this trypanosome also, 

 though here it was very difficult to obtain a first growth from 

 the blood on their blood-agar medium ; once started, however, 

 it was kept alive through many sub-cultures, the optimum 

 temperature of growth being 25 C., and it was from these 

 sub-cultures that the infection was obtained which definitely 

 proved the organism to be the cause of the disease. In cultures, 

 as with Tr. Lewisi, short forms occur, and there is sometimes a 

 rosette formation with the flagella directed outwards ; agglutina- 

 tion phenomena are also observable in defibrinated blood. 

 Under unfavourable conditions involution forms occur, the 

 organism dividing frequently to form round flagellated 

 individuals. 



Nearly all laboratory animals are susceptible to infection, 

 and the duration of the illness corresponds to what has been 

 observed in the natural infection of these animals. The rat 

 has been largely used for experiment and usually succumbs in 

 about ten days, there being very few symptoms up till a few 

 hours before death. A very important fact has been observed 

 with regard to this animal, namely, that individuals which have 

 gone through infection with Tr. Lewisi and which are immune 

 are still susceptible to the Tr. Brucei; from this it has been 

 deduced that the two organisms are to be looked on as -distinct 

 species. 



Trypanosoma of Sleeping Sickness. Since the year 1800 

 the disease called sleeping sickness, sleeping dropsy, or negro 



