NAGANA OK TSE-TSE FLY DISEASE 657 



finally, that the transference of the smallest quantity of blood from an 

 affected, to a healthy animal originated the disease. He then proceeded 

 to investigate the part played by the tse-tse tly in the condition. He 

 found that if Hies taken from the fly belt, but which had not fed on an 

 infected animal, were transported to a place where nagana did not occur, 

 kept for a few days, and then allowed to bite susceptible animals, the 

 latter did not contract the disease — this result showing that it was not, as 

 had been supposed by some, a poison natural to the insect which was the 

 pathogenic agent. But if such a fly was allowed to bite a dog suffering 

 from the disease and then to bite a healthy dog, t"he latter contracted the 

 malady and abundant trypanosomes were found in its blood. Again, 

 threads dipped in the blood of an infected animal and allowed to dry 

 caused the disease in healthy animals up to, but rarely beyond, twenty- 

 four hours after being dried ; if, however, the blood were kept moist, then 

 it retained its infectiveness up to between four and seven days ; up to 

 forty-six hours living trypanosomes could be seen in the tube of the fly's 

 proboscis. Further, Bruce showed that infection did not occur by any 

 food or water partaken of by an animal while going through a fly belt, 

 for he took horses through such a region without allowing them to eat or 

 drink, and found that they still contracted the infection, if during their 

 few hours' journey through the belt they had been bitten by the tse-tse 

 fly. Finally, he showed that if flies were taken from an infected area to 

 a healthy one a few miles off and allowed to bite infected animals, the 

 latter contracted nagana. 



By those experiments it was thus determined that nagana could be 

 transmitted by the blood of the infected animal— that is, without the 

 agency of the fly ; that the latter had no inherent power to produce the 

 disease ; that it could, however, by successively biting infected and 

 healthy animals, transmit the disease to the latter ; and that specimens 

 of the insect caught in infected areas harboured the parasite and were 

 thus infective. The question remained as to how the flies might become 

 infected in nature. It had been observed that in districts where the tse- 

 tse fly lived, the prevalence of the disease in imported animals was related 

 to the presence in the locality of wild herbivora. Bruce now found that, 

 if considerable amounts of the blood of the latter were taken to another 

 locality and injected into dogs, these in a proportion of cases contracted 

 nagana, and from this he deduced that the wild animals harboured the 

 parasites in small numbers in their blood and thus kept up the possibility 

 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. It is 

 doubtful whether the glossina acts as a mere mechanical carrier, as there 

 is evidence that the trypanosome undergoes a cyclic development in the 

 body of the insect. 



The Tr. brucei (Fig. 196), according to Laveran, measures in the horse 

 from 28 to 33 /t long and from l - 5 to 2"5 ii broad ; in the rat and dog it is 

 somewhat shorter. Jt 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 five to 

 six 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" to 7° C, but, like the 



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