586 Veterinary Medicine. 



stages of growth of the parasite appear to be the same as de- 

 scribed for the Trypanosoma Equiperdum of Dourine, to which 

 accordingly the reader may turn for description. The distinction 

 from that parasite is to be found mainly in the pathogenesis. In 

 this respect it should be noted that the parasites are strongly at- 

 tracted by the red globules, upon which they fasten themselves by 

 the blunt ends, shaking the cell in the most vigorous manner and 

 even breaking pieces off and carrying them away. They are most 

 strongly attracted by the concave part of the disc, and when 

 there are rouleaux they will bore between the globules and even 

 push them apart (Evans). 



The appearance of the disease at the conclusion of the rainy 

 season when the waters dry up and become foul, has led to the 

 idea that the parasite lives in waters, but as this is also the time 

 of the great swarming and activity of flies, and as the trypano- 

 soma is found in the bodies of tabanidse and hippoboscidae that 

 have bitten affected animals (Ljngard), and as horses crowded 

 together so that the fly with piercing apparatus still wet can pass 

 from horse to horse (Evans), the opinion has grown that it is a 

 compulsory parasite which is transmitted through the bites of in- 

 sects. In 1880, Griffith Evans found that the native Hindoos at- 

 tributed the disease to the bites of a very large brown fly which 

 was active in July (probably a tabanus), in 1897, Pease identified 

 the incriminated fly as the tabanus tropicus. Finally, Rodgers, 

 in 1 90 1, took flies that had been on surra horses, kept them 4 

 days or longer and found that their bites failed to produce surra ; 

 whereas those that were allowed to go directly from the sick to 

 the healthy animal produced the disease in the latter. The direct 

 experimental inoculation from horse to horse infallibly conveys 

 the disease so that the flies are not needed to pass the parasite 

 through an intermediate stage of its existence, but merely to 

 carry it. It follows that no particular fly is the bearer but any 

 insect may carry the infection from a bite or sore to inoculate it 

 on a sore or by a bite on a fresh animal. Different observers 

 have noticed the tendency to the infection of dogs and other ani- 

 mals that fed from rubbish heaps, or upon the carcasses of ani- 

 mals dead of surra, suggesting at once the intervention of the 

 swarms of flies that congregate at such places. This is probably 

 another example of the shrewd insight of the common mind, as 

 in the case of the tick-borne Texas fever. 



