10 Dec, 1917.] Fluke in Sheep. 707 



eveu in a foetus, and in the lieart and largo blood vessels of adult animals 

 and man. 



Infection of the sheep generally occurs in mid and late winter, deaths 

 occurring from January to September of the following year. At the 

 end of some six to twelve weeks the fluke is able to produce eggs, making 

 the whole life-cycle possible in a minimum of thirteen weeks in a wet 

 summer — and it has been shown that flukes may retain their full vigour 

 at least thirteen months, aiul, perhaps, up to three years. 



The species of snail necessary as an intermediary host varies in 

 diiferent countries — thus, in Europe, it is Liimuva truncatula, as proved 

 definitely by the classical feeding experiments of Thomas and Leuekart, 

 and Limnora percgra. also as shown by Leuekart. In some countries, 

 other species of Limnasa, and perhaps, other genera, are implicated. In 

 Australia, although Kedias and Cercarise, from a number of species 

 belonging to several genera of fresh-water snails, are known and recorded, 

 there is no record of any feeding experiments yielding positive results, 

 such as are essential to finally prove the exact relationship of these RedisB 

 and Cercariw to the life history of FascioJa hepatica. 



We are, therefore, still unable to say. with certainty which species is 

 the intermediarj' host of the common liver-fluke, although undoubtedly 

 it is some species of small fresh-water snail, probably Bulinufi ienuis- 

 triatus, B. brazier, and Ancylus tasmanicus, as the observations of 

 Cherry, Fielder, Cobb, and others suggest. 



It may be readily understood that there are many chances against 

 any one egg completing its life cycle, but the large number of eggs pro- 

 duced by each fluke (45,000 as a minimum), the power possessed by the 

 eggs of remaining dormant for months if they fall on dry soil, the in- 

 crea.se in number of individuals in ertch generation within the snail 

 host, the very considerable resistance of snails, even of some fresh-water 

 snails, to partial or temporary desiccation, and the fact of encystment on 

 grass or in the snail, are all factors of much importance in enabling the 

 fluke to evade untoward conditions. 



It will be seen from the preceding sketch of the life history of the 

 fluke, that the conditions for propagation of the disease in any area are 

 f 1) the presence of eggs of the fluke, (2) Avct. swampy or marshy ground 

 or pools, or slow streams, in which the eggs hatch, (3) the presence of 

 the intermediary snail host in the area, and (4) the presence of sheep 

 or other herbivorous mammals, which may swallow the encysted parasite 

 and so become infected, and in which the fluke may reach sexual 

 maturity. 



(2) THE EFFECTS OF FLUKE ON THE LIVER. 

 By H. R. Scddon, B.V.Sr. 



As mentioned by Dr. Sweet in the preceding section of this article, 

 infection of the liver may, apparently, take place in two ways. These 

 are by the young flukes (1) passing from the intestine up the h\h duct 

 to the liver, or (2) getting into the portal blood circulation from the 

 stomach, and so being carried to the blood vessels in the liver. The 

 former has been previously thought to be the common method here, but 

 it would appear that the latter (infection through the blood circulation) 

 has certainly taken place in the particular type of the disease observed 

 in Victoria this year. 



