556 Dr. H. L. Duke. Some Observations on [Aug. 16, 



and examination of two blood films from each of A, B and C proved negative. 

 Trypanosomes identical morphologically with T. pecorum appeared in the 

 blood of Monkey 359 on November 13, 1911, 23 days after the inoculation 

 of the bushbuck blood and 33 days after the last feed of Box 253. From 

 November 1 to 10 inclusive the monkey was not examined. The trypano- 

 somes might thus have been derived either from the bushbuck or from the 

 positive fly of Experiment 253 ; in each case with a long incubation period. 



The negative evidence of Goat 484 and of the blood films, together with 

 the fact that such a trypanosome has never before been recovered from wild 

 flies in the Mpumu district, makes it almost certain that the trypanosomes in 

 Monkey 359 came from Fly 9 of Table III. The curious inability of labora- 

 tory-bred flies to infect monkeys with T. pecorum, even though showing a 

 well marked proboscis infection, has been mentioned by Fraser and myself, 

 and is also evident in Table III. 



It is thus possible that the unusual swarming condition of the sucking 

 stomach to be described in Fly 9 of this table may have a definite develop- 

 mental significance in T. pecorum. 



It may be noted that the trypanosomes in the monkey were characterised 

 by a large vacuole posterior to the trophonucleus. This was very striking 

 in the fresh state, even with low magnifications. This condition was lost in 

 a subinoculated white rat. 



A further observation which to some extent provides a parallel for the 

 long incubation period, supposing Fly 9 to have been responsible for the 

 infection, is afforded by Experiment 644. In the case of this monkey, 

 inoculated from a goat suffering from T. pecorum, trypanosomes first 

 appeared in the monkey's blood 26 days after inoculation. The blood in 

 this case was examined daily. It is to be noted also that T. pecorum may 

 often not be seen for days in monkeys' blood, and when present is frequently 

 in very scanty numbers. 



The curious backward condition of Fly 12 is interesting. Similar instances 

 occurred in flies infected with T. nanum* but then there was a possibility of a 

 secondary "pick up" of trypanosomes from the calf employed. In the 

 present" instance, as the monkey of Experiment 247 never became infected, this 

 explanation is not available. 



It is to be regretted that in only three cases were the salivary glands 

 obtained in the above positive flies. In all these the glands were negative. 

 In this respect also T. pecorum shows resemblances to T. nanum. 



A remarkable feature of the above table is the fact that no proboscis 

 infections were obtained before the 76th day of an experiment. This delay 

 * "Transmission of T. nanum," 'Eoy. Soc. Proc.,' 1912, B, vol. 85. 



