XVIIl] TRANSMISSION 345 



but produced no infection, thus shewing that these animals are 

 only slightly susceptible to this trypanosome. 



G. morsitans is also capable of transmitting T. dimorphon, 

 and thus four species of tsetse-flies in West Africa are all 

 efficient intermediate hosts for the parasite. 



The experiments with regard to the infection of the fly are 

 somewhat inconclusive, but from an examination of " wild " 

 tsetse it appears that longipalpis is the most often infected, 

 then tachinoides, whilst the proportion of palpalis containing 

 dimorphon is very much less, being only about one per cent. 



In Dahomey, the negative period of incubation in the fly is 

 said to be more than 18 days, but as Bouet and Roubaud worked 

 entirely with wild flies the exact period could not be decided. 



The infection in each species of fly is what is known as 

 " total." The trypanosomes become established in the hind 

 intestine and gradually extend forwards until they reach the 

 proboscis, when they become fixed and assume the Leptomonas 

 or Crithidial form. These proboscis forms of dimorphon may be 

 distinguished from those of congolense by the frequent occur- 

 rence of giant forms like those of cazalboui, but differing in the 

 flattened appearance of the posterior prolongation. The inocu- 

 lation of intestinal forms produced no infection, whereas when 

 the proboscis was inoculated a positive result was obtained. 



It is evident, therefore, that the evolution of T. dimorphon 

 in Glossina longipalpis, tachinoides, palpalis, and morsitans, 

 respectively, is of the usual type, first a multiplication of try- 

 panosomes in the intestine, during which period the fly is non- 

 infective, followed by an invasion of the proboscis where the 

 Leptomonas or Crithidial stage is gone through, after which 

 the fly becomes infective. 



REFERENCES. 



Bouet (1907). Ann. Inst. Pasteur, vol. xxi. p. 474. 



and Roubaud (1910). Bull. Soc. Path. Exot. vol. in. p. 722. 

 Dutton and Todd (1903). Liverpool Sch. of Trop. Med. Memoir xi. 

 Laveran and Mesnil (1904). Compt. Rend. Acad. Sci. vol. cxxxvm. p. 732- 

 Montgomery and Kinghorn (1909). Lancet, Sept. 25, 1909. 

 Yorke and Blacklock (1911). Ann. Trop. Med. and Parasit. vol. v. p. 

 413 and vol. vi. p. 107. 



