Diseases of Domestic A nimals in Nyasaland. 9 5 



It will be seen from the above table that it was not until the last experi- 

 ment that the labial cavity and hypopharynx were examined separately. In 

 the previous experiments the presence or absence of trypanosomes in the 

 proboscis as a whole was noted. 



In the first two experiments, only a single infected fly was found in each. 

 In Experiment 1777, 11, and in 1784 as many as 20 were found. 



In regard to the number of trypanosomes in the labial cavity, this may 

 vary greatly. Sometimes the lumen of the tube will be seen to be densely 

 crowded ; at other times a single colony will be seen. For example, in 

 Experiment 1777 the first infected fly, dissected on the 21st day, is noted to 

 have had the lumen of the proboscis swarming with clusters of torpedo- 

 shaped flagellates attached to the labrum by their flagellar ends, a few 

 swimming free. In the seventh infected fly, dissected on the 30th day, only 

 three colonies, in the eighth one, and in the ninth two small colonies, are 

 noted. In the same way the hypopharynx may contain few ; at other times 

 it is seen to be densely packed with swarms of actively moving trypanosomes. 

 In unstained specimens the difference in size and shape between the 

 trypanosomes in the labial cavity and those in the hypopharynx is quite 

 manifest. 



It may be stated here that, exceptionally, flagellates may be seen in the 

 oesophagus, or that part of the alimentary tract anterior to the pro- 

 ventriculus. Among the 46 flies described above, this was noted twice. In 

 the first instance they are reported as being very scanty, in the second as 

 being active and in large numbers. 



But from Table III the broad fact stands out boldly — that in this species 

 of trypanosome the development is confined to the labial cavity and hypo- 

 pharynx, and does not take place in any other part of the fly. 



The Type of Trypanosomes found in the Infected Flies. 



No attempt has been made by the Commission to study the development 

 of T. caprce in G. morsitans in the earliest stages. This can only be done if 

 a large number of laboratory-bred flies are "available, and this was not the 

 case at Kasu. 



Plate 8 represents some of the developmental forms found in the labial 

 cavity and hypopharynx of infected flies. 



Fig. 1 represents a torpedo-shaped organism taken from a single cluster 

 growing near the bulb on the 19th day after the first infected feed. 



Figs. 2 and 3 are similar shaped flagellates, also from a single group 

 growing near the bulb on the 21st day. 



Figs. 4-10 are drawn from 24-day flies. 



