Infectivity of Glossina morsitans in Nyasaland. 423 



third on a goat. To ensure, as far as possible, that each animal was fed on 

 by every fly, the flies were fed nine times — three times on each animal. 



The number of flies brought up each day would probably average about 

 60, and as each animal was fed on by three cagefuls, then each monkey, dog, 

 and goat ran the gauntlet of some 180 flies. It is therefore impossible to 

 arrive at any very precise knowledge of the proportion of infective flies in 

 each cage. 



Infectivity of the Flies. 



As will be seen from Table I, every experiment, with the exception of one, 

 was positive, and on two occasions a goat was infected by all the four species 

 of pathogenic trypanosomes occurring in this neighbourhood. 



The Commission showed in a previous paper* that one in three of the 

 wild game found in this district is infected with trypanosomes, and recom- 

 mended that the animals should be destroyed. If this were done and a year 

 allowed to elapse, the proportion of infective flies then found would be an 

 index of the usefulness or futility of such operations. 



The Commission is of opinion that the wild game is the principal factor 

 in the spread of trypanosome disease, and that, for practical purposes, the 

 smaller mammals, birds, and reptiles need not be taken into account. 



The following table gives, in the first column, the date the first cageful of 

 flies was fed on the monkey, the second column the number of flies fed ; the 

 signs plus and minus show the result of feeding the flies on the monkey, dog, 

 and goat. 



The four species of trypanosomes carried by the " fly " in this district are 

 T. brucei vel rhodesiense, T. pecorum, T. simice, and T. caprce. The first and 

 second of these attack all three animals, the third the monkey and goat, 

 being harmless to the dog, whereas the fourth only produces disease in the 

 goat. 



Where no plus or minus sign occurs it means that an animal was not 

 available. For example, the experiment beginning on January 20 shows 

 that the monkey was infected by T. simice, the goat by T. brucei, and that 

 no dog was available. The experiment on February 21 shows that neither 

 the dog nor goat became infected by the bites of 170 flies, and that no 

 monkey was available. 



Supra, p. 277. 



