WORM NODULES IN AUSTRALIAN CATTLE. 339 



be able to pass into the egg of the tick. Further, the infection, 

 were the parasite tick borne, would be very much greater 



Leeches — These offer a possible intermediary. The fact, how- 

 ever, that the nodules are as numerous in dry districts, where 

 stations mainly depend on artesian bores for water, is against the 

 supposition. 



Water Crustacea, Etc. — These are, of course, also possible inter- 

 mediary hosts. 



Biting Flies. — These have certainly to be considered very 

 probable intermediaries. As against their operation is the likelihood 

 that, with such widely and easily spread insects, no part of Australia 

 (including Tasmania) would by this time be free of infection by 

 worm nodules ; and, further, one would expect a greater and 

 more general affection in individual animals. 



As regards all these possible conveyers, the age incidence is a 

 serious obstacle, and we are seriously inclined to suspect the inter- 

 mediation of some parasite more liable to attack the younger 

 animal. 



The Louse. — This offers the most hopeful possibility. It may 

 be one of the common species, or a new one hitherto undetermined. 

 The louse is a frequent parasite, especially on young cattle, 

 although rarely detected until the host becomes debilitated, when 

 it rapidly increases in numbers, as is the experience of every 

 stockman. Adult cattle are seldom under any conditions troubled 

 to the same extent. The louse is a parasite which, it must be 

 remembered, does not remain stationary. In cattle under station 

 conditions, which are seldom in actual contact with each other, 

 unless when travelled or yarded, the natural means of transmission 

 would be by intermediary of the ground, particularly the camps 

 and places of rest near water. Assuming the louse on swallowing 

 a larva or larvge loosens its hold and drops off — as we have observed 

 it does under experimental conditions after inoculation of larvae 

 into a " lousy " cow — on reaching a fresh host the place most readily 

 attacked would be where the skin comes in contact with the ground, 

 and where it is comparatively soft covering loose areolar tissue, 

 and, further, where there is little chance of the parasite being 

 licked off. The regions behind the shoulder and behind the stifle 

 meet these conditions, invariably and constantly touching the 

 ground when the bovine is recumbent. The fact that of the hind 

 quarters the right is the most frequent attacked, and that on this 

 the bullock generally rests, is also suggestive. If, therefore, the 

 louse injects the young filariae into the subcutaneous tissues imme- 

 diately after reaching a new host, the argument is fairly complete. 

 At any rate some definite explanation is required to account for 

 these filariae establishing themselves invariably in the same 

 regions ; and this uniformity of condition is very difficult to 

 understand on any other theory. 



