109 



4. Experiments with embryos: — 



Embryos of the three species kept in saline and tap water, 

 respectively, were added to sterilized horse-dung or sawdust and 

 placed on shaved areas of the skin of the two horses. 



In no case was any reaction produced in the skin of the 

 animals. 



5. Summary and discussion of the experiments: — 

 Experiments have shown that larvae of H. microstoma 



are capable of making their way into the subcutaneous tissues 

 of the horse through an incised wound in the skin. A certain 

 number of these larvae appear to be rapidly destroyed and 

 removed by phagocytes. Others are not so rapidly destroyed, 

 when they produce a necrosis of the surrounding tissue and 

 cells. As the larvae disappear they do not appear to leave 

 any worm canals in the necrotic areas. In the experiments 

 a tissue reaction was produced which is essentially the same 

 as that seen in granulomata occurring under natural condi- 

 tions. No granulomata were produced after allowing flies to- 

 bite the horse. When larvae were added to a lightly scarified 

 area of skin they appeared to be incapable of penetrating the 

 tissues; at least no tissue reaction which might suggest such 

 a penetration was produced. 



Larvae of H . muscae possessed the power of making their 

 way into the subcutaneous tissues, but only a very slight 

 tissue reaction was produced, and this quickly disappeared. 

 When they were added to the conjunctival sac they produced 

 no reaction. The larvae did not appear to be capable of 

 penetrating the lightly scarified skin, nor the moistened, 

 uninjured skin. 



Larvae of H. megastoma produced a typical granuloma 

 in one animal, but failed to produce the same reaction in the 

 other animal. The microscopic appearances of the granu- 

 lomata produced were exactly similar to those seen in lesions 

 occurring uncfrer natural conditions. Those larvae that were 

 not rapidly destroyed and removed produced typical necrotic 

 areas in which the degenerating larvae persisted for some 

 time, and after their disappearance very definite worm canals 

 were produced. The lesion, however, did not possess a marked 

 chronicity. The larvae produced a conjunctivitis in both 

 animals. They did not appear to be capable of penetrating 

 the moistened or scarified skin. 



The granulomata produced with larvae of both H. micro- 

 stoma and H . megastoma were comparatively small, and 

 showed little chronicity. Likewise, the conjunctivitis produced 

 by the larvae of H. megastoma was not of a very severe 

 character. The larvae of H . megastoma, when they produced 

 a granuloma, appeared to be better preserved than those of 



