32 EXPERIMENTS WITH CERTAIN DIPTERA. 



The possibility of direct transmission has not been 

 overlooked but it is considered highly improbable. Sub- 

 cutaneous injection of larvae, smearing them on the skin 

 and drenching them to a calf in milk have been tried un- 

 successfully by several investigators. Various' theories 

 have been put forward as to the intermediary host. The 

 idea that it might be (1) a carnivorous animal (Gibson 

 1893), (2) a leech (Gilruth and Sweet, Breinl), (3) a crus- 

 tacean (Cleland and Johnston, Breinl), has each been 

 suggested and rejected with little attempt at investigation.* 

 The theories that lice and flies are likely transmitters have 

 received more attention. Gilruth and Sweet (1911) con- 

 sidered that the calf louse Hcematopinus vituli L, presented 

 the most hopeful possibility. Later, however, as a result 

 of their experiments they were compelled to abandon the 

 idea that either of the cattle lice, H. vituli or H. eurystemus, 

 could act as a means of transmission of 0. gibsoni (1912). 



With regard to the fly theory, the most important work 

 has been carried out by Cleland who examined numerous 

 Stomoxys calcitrans after they had been allowed to feed on 

 fresh nodules. Living Onchocerca embryos were found 

 in one case on the third day after feeding (1914). Attempts 

 were also made by the same author in conjunction with 

 Dodd and McEachran (1917) to infect cah^es by exposing 

 them to the attacks of certain insects. Stomoxys caJcitrans, 

 Tabanids and mosquitoes {Culicelsa vigilax and Scutomyia 

 ■atripes) tested thus all gave negative results. 



Breinl examined Tabanids, Stomoxys calcilrans and 

 several species of mosquitoes fed over nodules, all with 

 negative results (1913). 



McEachran and Hill (1915) carried out work similar 

 to Breinls using Stomoxys calcitrans, Lyperosia exigua, 

 several species of Tabanus and Silvius and also Hcemat- 

 opinus tubercukitus (buffalo louse), but were unable to shew 

 any infection. 



The two similar experiments carr'ed out in Darwin by 

 McEachran and Hill (1915) and by Dckinson and Hill 

 (1917) have not lent supj)ort to the fly theory (Hill and 



♦Miss M. Henry has apparently examined Cladocera as possible 

 transmitters (P.R.S., N.S. Wales, 52, 1918, p. 463). 



