344 TRYPANOSOMA DIMORPHON [CH. 



Morphology of the parasite. In the fresh state, the dimorphic 

 nature of this species is easily recognisable. The most common 

 forms are only 12 to 14 microns in length and i micron in 

 breadth, with a rounded posterior extremity and a body which 

 gradually tapers towards the anterior extremity. These short 

 forms present a somewhat characteristic movement ; after 

 progressing forward for some little distance, wriggling after 

 the manner of a tadpole, they stop abruptly, and then move 

 on again in the same fashion. The undulating membrane is 

 very slightly developed. 



The long forms of dimorphon are less common than the pre- 

 ceding and may occasionally be absent. They range from 20 

 to 25 microns in length, by 1-5 microns in breadth. The 

 undulating membrane is only slightly developed and the 

 parasites, although more active than the short forms, do not 

 present as lively motions as T. brucei. 



These two forms are connected by intermediate stages, and 

 therefore the short trypanosomes might be regarded as a 

 young form of the large, were it not for the fact that they both 

 reproduce by longitudinal fission. 



In Giemsa-stained specimens, a remarkable feature of 

 dimorphon is the extremely dense blue colour of the protoplasm. 

 The kinetonucleus is situated close to the rounded posterior 

 extremity. The undulating membrane is never very marked 

 and in every case the protoplasm is continued along to the 

 extremity of the flagellum. This latter feature, together with 

 the dimorphism, is very characteristic. Division is of the 

 usual longitudinal type. 



Mode of infection. Bouet, in 1907, succeeded in transmitting 

 T. dimorphon by the bites of Glossina paipalis that had fed on 

 an infected animal 24 hours previously. In this experiment 

 the transmission was merely mechanical. 



In Dahomey, Bouet and Roubaud have demonstrated the 

 part played by G. paipalis, tachinoides and longipalpis in the 

 transmission of this parasite. Paipalis captured in nature, 

 were fed on two dogs, a sheep, and a kid, and these animals 

 became infected with dimorphon after incubation periods vary 

 ing from 14 to 20 days. The same flies were fed on guinea-pigs 



