202 VETERINARY LECTURES 



plished outside the body of the sheep, or host {Plates XXIV. and 

 XXV., showing the various stages through which it passes). The 

 flukes are bisexual, having both male and female organs in one 

 body, and are generated from little eggs. These eggs are developed 

 inside the parent fluke, which lies in the bile-ducts of the liver of the 

 host, and are ejected from the parent by one of its openings and 

 carried by the bile to the intestines, and there eventually carried, 

 ejected, and deposited on the ground in the droppings. As many as 

 200 flukes have been counted in one liver, whilst the number of eggs 

 generated by these has been reckoned at 7,400,000, or about 40,000 

 to each fluke. The eggs are about T §^ of an inch long and ^J^ of 

 an inch broad. Mr. A. P. Thomas's summary of the life-history is 

 as follows : 



' The adult fluke in the liver of the sheep produces enormous numbers of eggs. 

 which are distributed with the droppings of the sheep. If these eggs have 

 moisture, and a suitable degree of warmth, they continue to live, and in each is 

 formed an embryo. The embryo leaves the egg, and swims in search of the 

 particular snail, Limnceus truncatulus, within which its future life and growth 

 take place. The embryo bores into the snail, and then grows into the form which 

 is called a sporocyst. The sporocyst gives rise to the second generation. This 

 is known as redia. The redice, in turn, produces the third generation, which has 

 the form of a tadpole, and is called cercaria. The cercarice quit the snail, and 

 enclose themselves in envelopes, or cysts, which are attached to the grass. When 

 the grass to which the cysts adhere is eaten by the sheep, or other suitable host, 

 the young liver fluke comes out of the cyst and takes up its abode in the liver of its 

 host, and the fatal circle is thus completed. It will be seen, therefore, that 

 the fluke disease is one which alternates between a particular snail and the sheep. 

 A sheep cannot take the infection directly from another sheep, nor can one snail 

 take it directly from another snail. The sheep, by spreading the eggs of the fluke, 

 gives infection to the snail, and the snail, in turn, by harbouring and distributing 

 the cercarice, conveys the infection to the sheep. 



' The conditions necessary for the existence of liver-rot in any given locality 

 are as follows : 



' 1. There must be fluke eggs on the ground. 



' 2. There must be wet ground, or water, during the warmer weather, for the 

 eggs to hatch in. 



' 3. A particular snail, called Limnceus truncatulus, must be present. 



' 4. Sheep, or other animals, must be allowed to feed on the same ground 

 without proper precautions being taken. 



