352 TSETSE FLIES 



In the public speeches of Dr. Warrington 

 Yorke much importance has been attached to the 

 theory that by " driving back " Africa's magnifi- 

 cent fauna, only a portion of which, as he himself 

 admits, has shown itself to afford hospitality to 

 the sleeping sickness parasite, the main reservoir 

 of infectivity will be removed ; but I cannot 

 understand how this portion of the case can 

 possibly be considered (viewed from the stand- 

 point of our present knowledge) to have been fully 

 made out. To begin with, we have, so far as I 

 am aware, no evidence of the role played as hosts 

 of disease by the hundreds of species of diurnal 

 birds commonly found in the affected portions of 

 the sub-continent ; moreoever, if we were to dis- 

 miss them one and all from consideration, we must 

 not forget that in some cases where parasites have 

 been discovered in the blood of certain of the 

 four-footed types examined, it was found, I under- 

 stand, that they were so few and far between that 

 their discovery was only effected after long and 

 patient search. One may thus, I think, form, with 

 some slight approximation to certainty, a faint 

 idea of how many times the animal might be 

 bitten without infecting the puncturing fly at all. 

 It is perhaps possible that the beast might pass 

 from infancy to old age without bestowing one of 

 its rarely-occurring parasites upon a single tsetse. 

 Again, although, I doubt not, it will be said that 

 the present is no time for temporising, and that 

 every potential source of infection must be ruth- 

 lessly " driven back," I cannot refrain from 

 pointing out our entire want of evidence that the 



