_ Pass through their larval stages in Musca domestica, 
120 
ar 
nucleated cells, is due to the reaction of the tissues against an 
invasion by a larval or adult metazoan parasite, usually a 
Nematode. There seems to be no reason to suggest that 
“swamp cancer” offers an exception. 
It is now known that these lesions in the skin and external 
mucous membranes of the horse are most commonly due to à 
larval Habronema, and there is strong presumptive evidence 
that “swamp cancer" is due to a similar larva 
large, chronic lesions. Their small size appears to depend 
upon the few necrotic areas present and a resistance on the 
part of the animal which is apparently absent in those animals 
which develop large, chronic lesions. : 
xperimentally it has been shown that larvae belonging 
ally it has also been shown that apparently the tissues of some 
animals offer a strong resistance to the presence of these es ai 
and are capable of quickly destroying them before they are 
able to produce much reaction. It will be seen, therefore, pre 
the possibility is that “swamp cancer" may be due to any pus 
of the three ies of Habronema. Evidence is not in free 
however, of : tha probability ot “swamp cancer" being due ns 
eA of either H. muscae or H. megastoma. These two "T 
ble 
mp 
be 
thi : an 
5 fly 1s not usually to be found far afield, it seems proba 
that it is iated with the occurrence of “swa 
e 
species 
ns there is more 
inoculated with these 
