144 TRYPANOSOMIASES OF RHODESIA. 



nor rabbits infected with this virus have shown the same en- 

 largement of the head. 



In my animals sonmolence has seldom been noted, and the 

 naniL- " sleeping sickness " could not 'be apphed to the disease in 

 them. I may mention that I have, more than once, been struck 

 by the close resemiblance between such infected rabbits and those 

 dying at the same time from rabies. 



The question of the method of transiiiis'sion of trypanosomes 

 is of the utmost importance, and. unfortunately, is the one con- 

 cerning which the greatest uncertainty exists. I may be for- 

 given for dealing with it at some length. 



It will be remembered that !Montgomer}' and Kinghorn ex- 

 pressed the opinion that the animal trypanosome which they en- 

 countered at Broken Hill could be transmitted not only by Glossiiia 

 inorsifaiis, but also by Sfoiiioxys calcitraiis and a species of 

 Lypcrosia. Such a suspicion caused considerable alarm, inas- 

 much as it upset the pre-existing theory of the strict interrelation 

 of the animal trypanosomiases and the " tsetse fly," and neces- 

 sitated immediate jirophylactic mieasures ; for the newly 

 incriminated flies were abundantly present throughout the 

 country and other parts of South Africa, and by no means as 

 restricted in distribution as Glossiiia niorsitaiis. Moreover, at 

 the time, no special embargo was placed upon " fly-struck " cattle, 

 Avhich were widely distributed and with the game constituted a 

 potential reservoir of virus. In Southern Rhodesia official regu- 

 lations were immediately enforced to deal with the situation, 

 preventing the movement of cattle out of " fly " areas and 

 quarantining large numibers of slaughter stock from the north. 

 Sujch restrictions natu'rally caused great inconvenience and 

 financial loss to the stock-owning community, and gave rise to 

 vigorous protests from all sides, with the result that an extra- 

 orcHnary amount of evidence was advanced which emphasised in 

 a very marked manner the fact that, as far as the trypano- 

 somiasis of stock in Southern Rhodesia is concerned, a strict 

 inter-dependence exists between the disease and the '* tsetse 

 fly." 



I think I am correct in stating that up to the present, in 

 these territories, no case of animal trypanosomiasis has been en- 

 countered where the possibility of previous exposure to the bite 

 of the " fly " could be positively excluded. Moreover, in the 

 absence of the " tsetse " the disease has failed to spread, in 

 spite of the prevalence of other biting flies, as, for example 

 Sfovio.vys, Tabanidrr. Hippohosccc, HccmatopotcB, etc. 



At the la'boratories at Salisbury Stoinoxys are present at 

 some times of the year in vast numbers, and I have had infected 

 animals standing side by side with healthy susceptible animals 

 for months without one of the latter becoming infected, although 

 there was no reason why mechanical transmission should not 

 have occurred ; in fact, methods were adopted to encourage it. 

 Moreover, in experimental small animals the number of try- 

 panosomes in the peripheral blood is always far greater than in 



