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A. — Introduction. 



In 1916 the present writer recorded the occurrence in 

 Australia of a granuloma which, in his experience, was most 

 frequently found affecting the external genitalia of the horse. 

 The condition was found to be of rather infrequent occurrence. 

 ' It was first observed in 1912, and from this time onwards an 

 occasional specimen was obtained. It was not until the early- 

 part of 1914 that the granuloma was found to be due to a 

 larval Nematode. 



These preliminary observations were recorded, and up till 

 that time no record of the occurrence of the condition in 

 Australia had been made. 



The condition was described under the name of hab- 

 ronemic granuloma, and the opinion was expressed that it 

 was none other than the granulomatous affection found com- 

 monly in the horse and ass in various parts of the world, 

 and known usually as "summer sores," or "granular 

 dermatitis." An hypothesis was advanced that a biting fly 

 was in some way responsible for the introduction of the larvae 

 into or beneath the skin of the animal, and as a larval 

 Habronema had been described as occurring in Stomoxys 

 calcitrans, it was thought that this fly was incriminated. 



The present communication recapitulates the original 

 observations, and records further observations and experi- 

 ments. After an investigation into the life-histories of the 

 three species of Habronema found in the stomach of the horse, 

 and after an experimental investigation of the cause and 

 nature of the tumours, the original hypothesis has now to be 

 considerably modified. 



Since the disease was first recorded as occurring in Aus- 

 tralia, Lewis and Seddon (1918) have recorded the occurrence 

 of the condition in the region of the conjunctiva of horses 

 in Victoria. 



Place (1915) in a previous publication had attempted to 

 prove that the occurrence of malignant neoplasms in the orbit 

 of the horse was commonly associated with the presence of 

 larval Nematodes in this situation, and although he incrimin- 

 ated a larval Habronema, there was no record of the worm 

 having been isolated and identified. 



A further macroscopic and microscopic study of the 

 granuloma occurring in horses in the northern parts of Aus- 

 tralia, and commonly called "swamp cancer," has been made, 

 and the observations are outlined below. 



The literature bearing on the subject of "summer sores" 

 and other similar conditions is reviewed and discussed in the 

 following paper. 



