PARASITIC DISEASES OF THE LIVER. 



295 



the consumption of green fodder, or through the ingestion of water 

 containing cercaria. The disease may be contracted very rapidly. 

 Many animals left in the fold on account of indisposition, or 

 of some other affection, or which have been carried by the shep- 

 herd because they were very lame (Hahn), have been observed to 

 escape distomiasis, while the whole remainder of the flock became 

 infested. 



From time to time it is observed in the hare, the stag, and mainly 

 in the deer ; these beasts lose flesh, become greatly emaciated and 

 die of marasmus. 



Ingestion and emigration of the hepatic fluke-worm 

 (Distoma). The infection of the flocks takes place during summer 

 and fall, up to the first frosts (Gerlach) ; the summer's heat is very 

 favorable to the hatching of the eggs, but the night frosts do not 

 destroy the larvae of the distoma (Friedberger), and the animals 

 may contract the disease during the last months of the year, even 

 in December. 



As we have already stated, this infection may take a very rapid 

 course : a quarter or half an hour's grazing in a meadow which is 

 invaded by these parasites is often suflicient. Sometimes successive 

 invasions are observed upon the same animals, or it may appear in 

 spells upon some groups of animals of the same flock. 



We have three theories before us concerninsj the mode of intro- 

 duction of the fluke-worms into the liver : 



1. The fluke- worms are said to reach the liver through the portal 

 system. According to Heller, it seems, indeed, to be in this way 

 that the invasion of the liver by the embryo of echinococcus is 

 produced ; this opinion, however, concerning distomiasis is not 

 based upon any fact. 



2. The embryos having become free by the digestion of their 

 covering membrane, would pass through the stomach and intestine, 

 and penetrate into the liver through its peritoneal coating, and 

 would finally settle in the biliary canals (Gerlach, Spinola, May). 

 Friedberger points out that the frequent existence of perihepatitis 

 is far from being a sure proof of the correctness of this hypothesis ; 

 the inflammation of the serous membrane which surrounds the 

 liver may just as well be produced by a centrifugal emigration of 

 the fluke-worms, by their sub-peritoneal progression, and by the per- 

 foration of the serous membrane from the inside outward. It is not 

 rare to find a fluke-worm's head protruding from the liver surface. 



