90 



must be referred to the original work. The conclusions deduced from 

 these experiments are stated as follows : 



" In order that G. morsitans may gorge itself, it is not necessary that 

 the liquid upon which it is feeding should be subject to positive 

 pressure. 



" It may be asked why these flies do not suck up extravasated blood, 

 offered to them in that condition, in a receptacle not covered by a 

 cutaneous membrane. We believe that the role of the latter is purely 

 mechanical ; that it serves solely to guide the effort of the fly, which 

 is accustomed to 'bite through a wall penetrable by its proboscis. 



" As regards the quantity of blood that Tsetse-flies imbibe at a meal, 

 the average amount that appears to satisfy their appetite and causes 

 the abdomen to become greatly swollen is, according to our experiments 

 (in the course of which the pressure of the liquid absorbed has varied 

 from 11 cm. to 4-5 cm.), from 0-056 c.c. to 0-06 c.c. Certain flies are 

 capable of imbibing as much as 0-091 c.c., but this is the maximum 

 observed by us. 



" We have succeeded in causing specimens of G. morsitans to imbibe 

 blood serum devoid of red corpuscles, but it is only when greatly famished 

 that they gorge themselves with this fluid. Similarly, they have been 

 given blood containing neutral red in a solution of 1 in 3,000, and 

 tartrate of soda in a solution of 1 in 20,000. The latter appeared to 

 have an injurious effect upon their digestive functions. 



" It has also been observed, on several occasions, that Tsetse-flies 

 imbibe blood more readily when its temperature is raised to 36 C. or 

 37 C. (96-8 F. or 98-6 F.) than when it is cooler. In the same way, 

 if it be desired to feed these insects in vitro several times in succession, 

 it is necessary to take certain aseptic precautions, for should the flies 

 imbibe blood already contaminated with a certain number of bacteria, 

 the multiplication of the latter continues in the alimentary canal, and 

 the insects soon die." 



CHAPTER IX. 



RELATION OF TSETSE-FLIES TO THE SMALLER ANIMALS. 



Mr. LI. Lloyd (89), writing on the bionomics of Glossina morsitans in 

 Northern Rhodesia, remarks that: "The dependence of the tsetse- 

 fly on the larger mammals . . . depends on the ability of the 

 smaller mammals, birds and reptiles to avoid the insect." " The 

 behaviour of some of the smaller animals when placed in a cage with 

 tsetse," continues Mr. Lloyd, " was studied in the laboratory. The 

 flies used were freshly caught, and most of the experiments were carried 

 out in a glass cylinder 10 in. high and 6 in. diameter." The following 

 animals were employed as subjects. Mammals : " An adult wild 

 rat " ; "A young wild rat, just weaned " ; "A burrowing rodent (a 

 species of MURIDAE) " ; "A very young specimen of another species of 

 MURIDAE " ; "A young wild mouse " ; "A mole rat (Georychus) " ; 

 " A species of dormouse " ; "A shrew (Crocidura sp.) " ; and " A 

 young banded mongoose (Crossarchus sp.)." Birds: "A fowl." 

 Reptiles : "A skink lizard " ; "A young gecko " ; "A chameleon." 

 Amphibians : " Two species of toad." 



After detailing results, Mr. Lloyd observes : " The conditions under 

 which the experiments were carried out were very artificial, the 

 animals, and still more the flies, being eager to escape. It is apparent, 



