1909.] Trypanosoma gambiense in Glossina palpalis. 407 



Summary of the Experiment which forms the Subject of this 



Paper. 



Before describing at length the experiment which forms the subject of this 

 paper, we may summarise it as follows: — 



1. On March 5, 1909, 60 Glossince palpalis caught on the lake shore were 

 placed in two cages, 30 in each. The flies were fed on two infected monkeys 

 for 2 days. They were then starved for 72 hours to get rid of mechanical 

 transference. The following 5 days they were placed on a healthy monkey, 

 and every successive period of 5 days, or thereabouts, on a fresh monkey, up 

 to 86 days, when the experiment came to an end. The result was, that the 

 first two monkeys remained healthy, but that all the following monkeys, up 

 to 75 days, became infected with Trypanosoma gambiense. 



2. If 7 days be deducted for the incubation period, then the flies first 

 became infected 18 days after their first feed on an infected animal. 



3. There is some evidence that among the 60 flies only 1 was infective. 

 "Fifty-four days after the beginning of the experiment each cage was placed 

 on a separate monkey. Up to that time both the cages of flies had been fed 

 on the same animal. Cage A contained, after 54 days, 11 flies. Cage B, 

 4 flies. Cage A continued to infect monkeys for 21 days more, making 

 a total of 75 days. Cage B did not infect. Again, as was natural, the flies 

 gradually died off during the experiment, and as each fly died it was carefully 

 dissected and examined for trypanosomes. Not a single trypanosome of any 

 kind whatever was seen in any dissected fly up to 75 days, when a fly died 

 in Cage A which was found to be swarming with trypanosomes similar to 

 Trypanosoma gambiense. After the death of this fly, Cage A ceased to be 

 infective, and when the experiment was stopped the remaining flies were 

 killed off and dissected, but among them not a sign of a trypanosome could 

 be seen. In the same way the flies remaining in the non-infective Cage B 

 were examined, with a similar negative result. 



4. Here follows an interesting and unique observation. A tiny drop of 

 fluid taken from the gut of the 75-day fly injected under the skin of a 

 monkey gave rise to Sleeping Sickness after an incubation period of eight 

 days. This, so far as we are aware, is the first time this has been recorded. 



5. It will be seen from the detailed experiment that the flies were starved 

 for three days between several of the experiments. This, of course, was to 

 get rid of the fallacy of mechanical transference. 



6. It may be said that perhaps these monkeys became infected by some 

 other means than the flies in the cage — for example, by other biting flies, or 

 by contact. To this it may be answered that there are more than 200 



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