33^ TRYPANOSOMA CAZALBOUI [CH. 



It is possible that this remarkable difference in the rate of 

 development may be accounted for by the difference in climate, 

 for Bamako, on the Niger, the locality where Bouffard performed 

 his experiments, is less than looo feet above sea-level, whereas 

 Mpumu is more than 4000. Moreover, the mean temperature 

 of Uganda is far below that of Bamako and the influence of 

 this factor is most important. 



After being ingested some of the trypanosomes remain in 

 the proboscis of the fly and change into Leptomonas or Crithidial 

 forms. These become attached to the walls of the labrum and 

 undergo rapid multiplication, resulting in the production of 

 large clusters of flagellates, which may almost obstruct the 

 cavity of the proboscis. Under the influence of the salivary 

 secretion some of these fixed flagellates develop into small 

 actively motile trypanosomes closely resembling the blood 

 forms. These free trypanosomes are found in the hypopharynx 

 and escape together with the salivary secretion when an infected 

 fly feeds on any host. 



Once a fly becomes infected it may remain infective for at 

 least two and a half months and probably for the remainder of 

 its life. If the air is very dry, however, the flagellates may 

 disappear from the proboscis and the fly cease to be infective. 

 Thus Bouet and Roubaud found that in Upper Dahomey 

 during the dry season about 50 per cent, of freshly caught 

 morsitans shewed infection of the proboscis, but when these 

 flies were kept and examined 20 to 31 days later the proportion 

 of infected flies was only two in thirteen, 



Roubaud has performed some very interesting experiments 

 on the effects of various conditions on the development of T. 

 cazalhoui in G. palpalis, which supplement the observations of 

 Bouet and Roubaud in Upper Dahomey. Twelve G. palpalis, 

 caught in nature, were placed in a dehydrated atmosphere. 

 Twelve hours later and twice in the three succeeding days they 

 were allowed to feed on a goat infected with T. cazalhoui. Four 

 days later they were fed on a healthy kid for two days. On 

 the ninth day the flies were dissected and found to be uninfected 

 and also the kid remained healthy. In another experiment 

 eight flies were fed for two days on the infected goat and then 



