89 



The surface of the blood in contact with the layer of skin is then 

 subject to the pressure of the entire column above it, which it is easy 

 to measure in millimetres. 



This arrangement enabled the Mission Scientifique not only to 

 estimate the tension that liquids must possess in order that Tsetse-flies 

 may gorge themselves, but also to measure the volume of blood imbibed 

 by the insects when feeding. 



In the course of a number of experiments, during which more than 

 100 G. morsitans fed from the apparatus, it was found by the investi- 

 gators, who employed citrated sheep's blood and fresh skin of the 

 common rat, that, in order that the flies may suck blood, the latter 

 needs to be subject to a pressure which is in reality very slight, 

 amounting to almost nothing. 



Fig. 8. Apparatus for feeding Tsetse-flies with extravasated blood, devised 

 by Drs. Rodhain, Pons, Van den Branden and Bequaert (Mission Scientifique 

 du Katanga. 116). 



A. Apparatus complete (half natural size). 



B - Lower part of apparatus (twice natural size), showing piece of skin 

 stretched over a rubber ring (b), which is fitted on to the lower end of a short glass 

 tube ; (a) rubber joint in upper end of short tube, carrying a graduated pipette. 



Subsequently Dr. Rodhain and his colleagues sought to determine 

 yet more precisely the limit of pressure to which a liquid must be 

 subject, in order that G. morsitans may suck its fill. With this end 

 in view, another little device, likewise extremely simple and highly 

 ingenious, was constructed, for the description of which the reader 



