70 THE PROBLEM OF HORSE SICKNESS. 



any time of the year, altliough more at certain seasons than at 

 others. In the case of the tsetse-fly disease, the game acts as 

 virus-carrier, or as a virus reservoir; in the case of ])iroplas- 

 moses, the recovered animal, cattle or horse, does. The reser- 

 voir for horse-sickness is not known. The analogy is, how- 

 ever, not a com])lete one. The Ijlood of trypanosome immune 

 game and that of ]Mroplasms immune animals, is infective w^hen 

 injected into suitable suce])tible animals ; that of immune horses 

 recovered from horse-sickness, however, is not. Perhaps this 

 ■could be explained by accepting that the virus only becomes 

 virulent after it has passed through the insect, similar to the 

 observation, made in b^.ast Coast fever, that blood of an ox 

 suiTering from East Coast fever can be safely injected into a 

 susceptible animal; the group of the brown lick, however, trans- 

 mitting the disease ])romptly. But here also the simile is not 

 quite analogous; the immune East Coast fe\er ox nn longer acts 

 as a reservoir. The experiments explained in connection with 

 o-oat and dog blood indicate that the virus can be ])resent in 

 one animal (goat) without being infective for the horse, l)ut 

 becomes so as soon as it has passed through a second animal (the 

 dog). If it could be shown that a winged insect becomes 

 infected on the reacting goat, most discrei:)ancies would dis- 

 a])pear. 



Quite a number of inoculation exjjeriments were under- 

 taken to find this reservoir. It is a fact that many birds live 

 or perch near rivers during the night, and many of them are 

 infected with bird malaria (Profcosoma ), which is transmitted 

 by Culicida?, a sure indication that they must be bitten l)y 

 mosquitoes. 



A bird might act as reservoir. During the horse-sickness 

 season we shot systematically a number of birds along the 

 Aapies River, and their blood was injected into susceptible 

 horses. There were a tota.l number of i;^/ injections, for 

 Avhich purpose the blood of 2/ birds was used, t'/rr. :— 



Elaniis ca-ntlcus (black-shouldered kite). 

 Ccrchncis nauniLinni (lesser kestrel). 

 Ccrchncis riipicoloidcs (larger kestrel). 

 Bnteo dcsertoniiii (steppe buzzard). 

 Bitteo jackal (jackal buzzard). 

 Scopus uiiibrcita (hammerkop). 

 Ceiitropits scnegalcnsis ( lark-heeled cuckoo). 

 Circus pygargns (Montague's harrier). 

 Ardea inelanoccpJiala (black-headed heron ~^ 

 Ardea purpura (purple heroir). 

 Turtur scucgalcusis (laughing dove). 

 Coluinba pJuconota (speckled pigeon). 

 Qlna capcnsis (Namaqua dove). 

 Asia nisuella (marsh owl). 

 Strix capcnsis (grass owl). 

 Bubo maculosus (spotted eagle owl). 



