THE DIGESTIVE ORGANS 203 



1 If any one of these conditions remains unsatisfied, there can be no fluke 

 disease or liver-rot in the locality. 



' If the eggs of the liver fluke are to be hatched, they must be in water, or, at 

 least, be kept moist, during some weeks of warm weather, or even some months if 

 the temperature be lower. If the eggs are once thoroughly dried, their vitality is 

 destroyed, the side of the shell being usually crushed in. A temperature of about 

 74 to 78 F. is the most favourable, and then the embryo is formed in about two 

 or three weeks ; with less warmth progress is slower, and with an average 

 temperature of 6o° the growth occupies two or three months. 



'Ground is often, with reference to the " rot," spoken of as "sound," or, on 

 the contrary, as "rotting." When the droppings, containing fluke eggs, fall on 

 to a field, the rain will distribute the eggs over the surface, washing them down 

 to the roots of the grass. If the soil be light or sandy, and porous, the land will 

 be " sound," for the water will filter into the earth, leaving the eggs on the surface, 

 where they will get dried, and so be destroyed. If, on the other hand, the soil is 

 heavy and clayey, so that the rain-water does not sink into the ground, but flows 

 along the surface, the ground is "rotting." For, as the water flows over the 

 surface, it carries the fluke-eggs along with it, and deposits them in ditches, holes, 

 marshy places, or furrows, where the water stands — all of them provinces where 

 the eggs will hatch. The obvious remedy for this evil is to drain the land 

 thoroughly and efficiently, and it will not only do much to prevent the rot, 

 but will have the further advantage of greatly improving the herbage. Where it 

 is not practicable to adopt this remedy at once, either salt or lime may be 

 scattered over its surface with advantage. Both these substances destroy the 

 embryos of the fluke, and, at a later period, the cysts, when attached to the grass ; 

 and, stiil further, they will destroy the snails, which serve as hosts to the 

 intermediate stages of the liver fluke. The freedom from rot of sheep which are 

 feeding on salt marshes is well known, and is now shown to be due to the 

 poisonous action of the salt on the embryos, sporocyst, rediat, cercaria, and cyst, 

 and to its similar action on Limnaus truncatulus itself. Even a weak solution 

 of salt and water (f per cent, of salt) proves fatal to this snail. Dressings of salt 

 have the advantage over lime in not spoiling the grass for immediate use, 

 whereas the latter will do so. It may, however, be better at times for the land 

 itself that lime should be applied. 



* There seems to be only this one snail in England which can serve as a host 

 to the intermediate forms of the liver fluke. Consequently, wherever this snail is 

 absent, there can be no liver-rot ; and if we could succeed in exterminating it, we 

 should render it impossible for the disease to exist in England. 



' It is naturally of much importance that salt or lime should be distributed 

 at the right time of the year, when fluke germs and snails are present in the 

 greatest numbers. The snail buries itself in mud or soil in the winter time, and, 

 owing to the cold, no embryos are hatched at that period. 



■ If the weather be warm in April, it is possible that a few may be brought out 

 towards the end of the month, but they will not be numerous. In May, however, 



