110 



H . microstoma found in the granulomata produced by the 

 latter. 



Under the conditions of the experiment the embryos of 

 all three species appeared to be incapable of penetrating the 

 skin of the horse. 



In these later experiments the results obtained in the 

 preliminary experiments were confirmed, viz., larvae of H. 

 muscae produced no conjunctivitis and no typical granuloma 

 in the skin, and the larvae of H. megastoma produced no 

 typical granuloma in the skin of the pony. 



The experiments have shown that the larvae of all three 

 species are capable of making their way into the subcutaneous 

 tissues when the injury in the skin has been deep enough to 

 include the corium. This migration in the tissues is probably 

 assisted by the oedema present. The larvae, however, do not 

 migrate for any great distance from the point of entry, in the 

 experiments only up to about 1 cm. The larvae do not appear 

 to be able to penetrate the tissues when the injury is confined 

 to the superficial epithelium. 



Considering the number of larvae inoculated, the 

 number of necrotic areas produced was small. This appears 

 to be explained by the probable escape of some of the larvae, 

 but more particularly by the early destruction of some of the 

 larvae. Tissues removed from five to six hours after inocula- 

 tion with larvae have shown the larvae surrounded by 

 neutrophile leucocytes, which attack and apparently quickly 

 remove them. Some of the larvae, however, appear to offer 

 more resistance or attract few or no neutrophile leucocytes. 

 These neutrophile leucocytes are not found in the tissues 

 removed from five to seven days after inoculation. The fact 

 that certain larvae of the same species appear to offer more 

 resistance to the attack of neutrophile leucocytes, or show less 

 positive chemotaxis, leads one to expect that certain strains 

 or varieties of the same species would be more likely to produce 

 granulomata under natural conditions. 



Discussion. 



That these larval Nematodes are the cause of the granu- 

 lomatous reaction there appears to be no possible doubt. 



Microscopical examination demonstrates that the larvae 

 soon after their introduction undergo degenerative changes. 

 There results an infiltration of the tissues with eosinophile 

 leucocytes and some proliferation of the fixed cells. Mono- 

 nuclear leucocytes are also attracted to the site. These 

 changes cause a tumefaction of the tissues which later usually 

 gives rise to a pressure necrosis in the skin or mucous 

 membrane. As the degenerative changes in the larvae progress 



