300 



Dr. H. L. Duke. Antelope as a [Apr. 20, 



That these animals may remain infective to fly for a period of at least 10 

 months after their original infection with T. gambiense has already been 

 proved by the study of the antelope in captivity at Mpumu. The animals 

 during this period remain in excellent health, as may be judged from the 

 fact that two young bushbuck have been born in captivity. 



The infectivity of these antelope to laboratory-bred G. palpalis gradually 

 diminished, until in March, 1911, it appeared probable that the parasites had 

 disappeared from their blood. Up to this date the evidence of infectivity 

 afforded by the presence of trypanosomes in the laboratory-bred G. palpalis 

 fed upon the buck, proved sufficiently regular without resorting to blood 

 injection. This latter method was considered a more searching and final test. 

 The experiments given in this paper represent the continuation of these 

 investigations from March, 1910, to January, 1912. During this period 

 laboratory-bred G. palpalis were fed upon the antelope, and their blood was 

 also tested by injection into susceptible animals. The injection test, 

 rendering possible the control of considerable quantities of blood, gradually 

 came to supersede the employment of clean flies. There is no reason to doubt 

 that an antelope infective to fly will also give a positive result upon 

 inoculation of its blood into a susceptible animal, and vice, versd. The 

 objection to the fly test consists in the small proportion of the laboratory- 

 bred flies used which are capable of harbouring the trypanosome. The 

 expenditure of time and trouble is also obviously far greater where a box of 

 flies is concerned than the mere injection of a few cubic centimetres of 

 blood. In several of the more recent experiments the flies were dissected 

 without ever having fed upon a clean susceptible animal, the presence or 

 absence of flagellates being sufficient evidence as to the infectivity of the 

 antelope. 



A few preliminary experiments were undertaken to determine whether 

 the animals had acquired any immunity to T. gambiense. These are included 

 below. This question has, however, only been superficially dealt with, as 

 the bushbuck selected as most suitable for the experiment became pregnant. 



Eeedbuck 2357. 



Original infection by laboratory-bred flies containing human strain of 

 T. gambiense, April, 1910. Latest evidence, previous to this discussion, of 

 the infectivity of this antelope was obtained in January, 1910, when it proved 

 infective to laboratory -bred G. palpalis. 



With the exception of Experiment 535, all these experiments were fed 

 upon fowls after their original feeds upon the antelope. 



