340 PROCEEDINGS OF SECTION D. 



The reasons we consider indicative of louse transmission may 

 be summarised as follows : — 



1. The constant infection of young animals (one to two 



years) to an extent equal with that of old. 



2. The frequent presence of lice on young animals in debili- 



tated condition due to any cause. 



3. The fact that in fat and adult cattle at abattoirs the 



nodules are practically never found smaller in size than 

 one and a-half centimetres in diameter, even after most 

 careful examination. This indicates a seasonal inci- 

 dence perhaps corresponding to a more or less recurrent 

 loss of condition, due to circumstances connected with 

 age and possibly food, thus favouring the entrance of 

 the worm. 



4. The situation of the nodules under the parts of the skin 



most readily attacked by the louse when picked up 

 from the ground. 



5. The gradual and slow advance of the infection from. 



north to south. 



Although, as above, the possibility of other blood-sucking 

 parasites, including the mosquito, acting as intermediary hosts 

 has not been overlooked, we are of opinion that at present the 

 louse is worthy of most attention for these reasons. Should 

 experiments on these lines which we are carrying out prove 

 negative, and another intermediary host require to be sought for, 

 complete proof will be a matter of difficulty, especially in Queens- 

 land, where it is impossible to be certain that experimental cattle, 

 unless imported from the far south, are, to commence with, free 

 from any nodule. 



Experiments thus far conducted on a heifer badly infested 

 with lice [HcBmatopinus vituli), which was injected on several 

 occasions subcutaneously with quantities of living and motile 

 larvae, eggs, etc., showed that as a result the adult lice drop off 

 the skin within a few hours. That this is not due to the larvae 

 alone, but rather to the distension of the subcutaneous tissues, is 

 proved by similar effects following injection of sterile normal 

 saline. That the lice may, however, ingest larvae, and that these 

 may live and grow in the louse, was proved by the discovery of 

 one living and motile larva in the body cavity of one of the lice 

 removed from the skin of the infected area twenty-four hours after 

 injection. This larva was entangled with the malpighian tubes, 

 from which it appeared to be trying to free itself. The passage of 

 lice to and from the injected area was prevented by a ring of tar 

 on a clipped surface. Lice from these inoculated areas have been 

 transferred to a calf, and the results are being awaited with interest. 



