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Lewis is also of the opinion that the evidence is strongly 

 opposed to the possibility of flies acting as the carrier of the 

 infection. This conclusion is based on the fact that the number 

 of biting flies in the Territory is considerable, but he has 

 observed no preference on the part of the flies as to the portion 

 of the horse to be attacked, whereas "swamp cancer" lesions 

 occur mainly about the legs and abdomen. He states, however, 

 that the biting flies present are chiefly Tabanidae, and it is 

 on observation of the presence and habits of these flies that he 

 draws his conclusions. 



Lewis concludes that the probability is that the virus 

 which causes the lesions "is normally a habitant of the 

 swamps." There seems to be some evidence to suggest that in 

 swampy districts horses are more prone to the affection. This 

 may possibly be explained, however, by the fact that in such 

 areas horse dung is liable to remain longer in a moist state 

 and be more attractive as a breeding ground for Stomoxys 

 calcitrans. He has demonstrated that the condition is not 

 contagious. His attempts to obtain micro-organisms by 

 cultural methods failed, and all attempts to reproduce the 

 lesions artificially by inoculation of portions of tumours from 

 horse to horse gave negative results. These results are impor- 

 tant, and are not incompatible with the hypothesis that the 

 lesions are due to some verminous infection. 



Lewis himself admits that "the inability to reproduce the 

 disease artificially from horse to horse suggests one of two 

 things — either the presence of an intermediate host or carrier 

 is necessary, or the appearance of the causative agent in the 

 horse is an accidental phenomenon. . . ." These conclu- 

 sions actively support the above hypothesis, for if the lesions are 

 due to a larval Habronema, the presence of an intermediate 

 host or carrier is necessary, and, moreover, the appearance of 

 the causative agent in the horse is, as far as we know, an 

 accidental phenomenon. 



"Swamp cancer" occurs in horses in the field, but when 

 these animals are brought in and placed on "hard food," Lewis 

 informs us, the tumours gradually disappear. If the granu- 

 lomata are due to a larval Habronema, this result is not very 

 surprising, for in this case there is present no virus or micro- 

 organism capable of multiplication in the tissues and of 

 causing a progressive infection. If "swamp cancer" is due to a 

 mould parasite, or some virus that is capable of multiplication 

 in the tissues, this result is remarkable. If this be the case, 

 it is also remarkable that necrotic areas do not increase in 

 number and occur in all stages of development. Further, the 

 failure of Lewis to transmit the disease from horse to horse 

 can be taken as very strong evidence against the probability 



