914 Transactions of the Socid;/. 



The disease was not observed to be contagious or infections in 

 the ordinary sense, but the possibility of its conveyance by means 

 of large brown flies was suggested. These flies attack the horses 

 so vehemently that the blood frequently streams from the bites ; 

 and the opinion that they propagated the disease was prevalent 

 among the natives. At the same time it was particularly noted 

 that at the outposts where the disease originated the water was 

 very impure. 



Evans discovered the parasite in all the diseased horses and mules 

 examined, in all diseased camels with one exception, and in the dogs 

 which had been subjected to experimental inoculations. The nature 

 of this and similar parasites forms the subject of my paper. 



Evans observes that when he first discovered the parasite he 

 thought it was a spirillum, but very speedily on closer examination 

 arrived at an opposite opinion. 



To him the organism presented the appearance, when fresh and 

 active, of an apparently round body, tapering in front to form a 

 neck and terminating in a blunt head. Posteriorly he describes a 

 tapering tail, from which there extended a long slender lash. At 

 the head end there appeared in one or two cases a circlet of 

 pseudopods, and as the body slowly died in serum it gave the 

 appearance of flattening out. After watching very closely all its 

 changes of form and movements Evans came to the conclusion that 

 there existed on either side of the body two fin-like papillae, one 

 near where the neck began and the other close to where the tail 

 began. In only very few instances, he adds, he was able to see 

 the four at once. He suggested that these processes were of the 

 nature of pseudopods. 



The parasite he describes as extremely active in its movements, 

 with an undulatory eel-like motion, progressing for the most part 

 head-end foremost but occasionally moving in the direction of the 

 lash when tugging at a corpuscle. In fresh blood these organisms 

 resembled spermatozoa in colour, but their peculiar characteristic was 

 the power they possessed of attacking and disintegrating the red 

 corpuscles. 



Occasionally two were observed to unite and swim off as one 

 body, but the mode of union was a disputed point. Evans thought 

 that they joined with their respective heads and tails in the same 

 direction overlapping each other, but Dr. Hay, to whom they were 

 shown, was of opinion that they fastened with their tails in opposite 

 directions. 



The parasites were not always present in the blood, but were 

 observed to come and go in successive broods. Evans referred the 

 organism to the late Dr. Timothy Lewis for his opinion as to its 

 nature. Lewis arrived at the conclusion that the parasite was 

 " more nearly related to that which he found in the blood of rats 



