66 SANITARY ENTOMOLOGY 



in analogy with what has been shown to occur in Filaria transmission by 

 mosquitoes, that the larvae of H: muscce can actively leave the proboscis 

 of the fly while the insect is sucking moisture from the mouth or lips of 

 the horse. There is already indirect evidence that this does occur. 

 The researches of Descazeaux (1915), Bull (1916), and Van Saceghem 

 (1917) have shown that the nematodes which occur in cutaneous granulo- 

 mata and so-called summer sores of horses are morphologically similar 

 to the larvsE of Hahronema muscce and in all probability*belong to this 

 or a closely related species. Recently Van Saceghem (1918) from investi- 

 gations carried out in Africa has reached the conclusion that the 

 nematode of summer sores is Hahronema muscce and that it is introduced 

 by flies. Larvae from infested flies were placed in the eye of a horse kept 

 in an insect-proof enclosure, with the result that conjunctivitis and 

 verminous nodules of the nictitating membrane developed. In another 

 experiment two wounds were made on the skin of a horse, one protected 

 against flies and the other left uncovered. The horse was placed in a 

 stable in which 20 per cent of the flies were infested with Hahronema. 

 The unprotected wound became transformed into a typical summer sore. 

 Bull (1919), who has made an extended study of cutaneous granulomata 

 of horses in Australia, believes that the larva of Hahronema megfastoma 

 are more often responsible for the production of habronemic granulomata 

 than either H. muscce or H. microstoma. 



Whether the Hahronema larva in summer sores are able to migrate 

 ultimately to the stomach and complete their development to maturity 

 remains to be determined. Bull (1919) thinks it unlikely that the larvae 

 of Hahronema are able to reach the alimentary canal from the submucosa 

 of the external mucous membranes or from the subcutaneous tissues, and 

 Hill (1918) also notes that the evidence of the occurrence of such a 

 migration is quite insuflicient. 



It is of interest to note that Hahronema muscce was known as a 

 parasite of the fly long before its relation to the horse was demonstrated. 

 Carter in 1861 was the first to record the presence of the nematodes in 

 flies, following which they were frequently observed by entomologists and 

 others who had occasion to examine the proboscis of the fly under the 

 microscope. 



Larval nematodes very similar to H. muscce have been seen in the 

 proboscis of Stomoxys calcitrans by Johnston and others. The researches 

 of Hill (1918) and Bull (1919) have shown that as far as their experience 

 has goiie the larvae in this species of fly have invariably been Hahronema 

 microstoma so that the occurrence of H. muscce in S. calcitrans appears 

 questionable. 



The fact that these more or less injurious parasites of the horse 

 depend upon flies for their existence is a point which may be added to 



