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tissues, it is not possible to say that it is never responsible for 

 the production of a habronemic granuloma. 



Clinical and experimental observations suggest that the 

 production of a habronemic granuloma depends in some 

 degree upon the susceptibility of the animal. It seems possible 

 that the presence in the subcutaneous tissues of larvae of any 

 of the three species of Habronema may set up a typical 

 granuloma, provided the animal possesses a susceptibility to 

 the particular species present. 



Experimentally it has been shown, for example, that 

 the presence of larvae of H . microstoma in the subcutaneous 

 tissues may set up a granuloma with typical caseous areas, 

 whereas, in the same animal, the presence of larvae of H. 

 megastoma or H . muscae may produce nothing more than an 

 acute inflammatory oedema, which quickly disappears, and is 

 followed by no subacute or chronic changes. 



It seems possible, further, that certain tissues may react 

 in such a way as to produce a habronemic granuloma, while 

 other tissues in the same animal show no such reaction. The 

 larvae of H. megastoma, for example, may set up a habronemic 

 conjunctivitis, but when present in the subcutaneous tissues 

 of the same animal little or no reaction is produced (vide 

 experiments) . 



Assuming that larvae of H. megastoma are responsible 

 for the production of habronemic granulomata, it seems 

 possible that certain varieties of the same species are more 

 likely to produce these lesions than other varieties. Certain 

 varieties, for example, may possess more vigour in penetrating 

 mucous membranes or moist surfaces, or they may possess 

 greater powers of adaptation. The same may be true for the 

 larvae of the other two species. 



Tt is possible that habronemic granulomata may be due 

 to the larvae of some unrecorded species of Habronema, 

 though it does not seem very probable. 



The fact that habronemic granulomata are to be found in 

 situations other than external mucous membranes led to the 

 advancement by the present writer of an hypothesis that 

 Stomoxys calcitrans was probably responsible for the inocula- 

 tion of the larvae into the tissues of the horse. It has now 

 been shown that S. calcitrans is the intermediate host of H . 

 microstoma, and that in the final larval stage the larvae of 

 this species show no longitudinal ridges in the cuticle. This 

 larva cannot, then, be responsible for the granulomata 

 observed by the present writer in Southern Australia. It is 

 possible that S. calcitrans may be the intermediate host of 

 some other species of~ Habronema, the larva of which shows 

 longitudinal ridges in the cuticle; but there is probably no 



