Treatment of Grass Land for Elimination of Disease. 81 



on conditions which cannot be wholly averted. Whether 

 these disease germs shall exist in numbers, sufficient to 

 seriously infest, may .possibly to some extent depend on 

 management, but while this may sometimes minimise the 

 contamination of the land and the risks of serious infestation, 

 it is to be feared that at present we are not in possession of 

 knowledge sufficient to ensure perfect purity of our pastures. 

 Unfortunately we are unable to determine that any given area 

 of grass land is polluted until its effects are manifested by 

 disease in animals grazing on it, and in case of most diseases 

 due to parasitic worms before there is any distinct manifestation 

 considerable numbers of animals have already become seriously 

 infested and further pollution is proceeding. It must be 

 remembered that such disease may not have been acquired 

 in the situation in which it is manifested. 



It is much to be regretted that we possess so little precise 

 knowledge of the life history of many of the parasitic worms 

 harmful to live stock. The immense aggregate loss attributable 

 to their action, which might possibly be averted by discovery 

 of the conditions essential to their existence in animals and on 

 pastures by suggesting appropriate means for breaking their 

 life cycles and purifying pastures, calls loudly for further 

 research, and we venture to express the view that to few more 

 desirable objects could portions of the Development Fund, 

 allocated to improvement of the conditions on which agriculture 

 is carried on, be applied, 



A forceful example of the value of scientific research in 

 this direction is supplied in the Report^ by Mr. A. P, Thomas 

 of his investigations resulting in discoveries which completed 

 our knowledge of the development of the fluke, the cause of 

 liver-rot, which thirty years ago decimated our flocks, but with 

 the ravages of which we are happily less familiar to-day. It 

 has been recogjiised that this parasite, after entering sheep, 

 cattle, and other animals in an immature form, gains the bile 

 ducts of the liver, setting up in this organ and elsewhere 

 disease, which baffles all attempts at cure, and emitting 

 innumerable eggs which are discharged with the faeces of 

 infested animals. It was demonstrated that, for the first stages 

 of development of the egg, moisture and some degree of heat are 

 essential. If these conditions exist on the spot in which an 

 egg is deposited, development may proceed to the stage at 

 which the immature parasite enters the body of a certain 

 fresh-water snail in which a period must be passed before it 

 becomes capable of infesting its ultimate hosts, the sheep, &c. If 

 this fresh-water snail is not availa1)le the fluke embryo perishes. 



' R.A.S.F,. Journal, Vols. 4?, 48, 44. 



