PREVENTIVE MEDICINE 339 



when badly affected fail to thrive, and in some seasons there is a 

 very high death-rate. The intermediate host of this tapeworm is 

 unknown. 



PREVENTIVE MEASURES. Prophylaxis should be directed to- 

 wards freeing the lambs of the worms and the destruction of the 

 latter. This is, however, by no means easily accomplished. A 

 common recommendation is to graze the contaminated land with 

 animals which are not susceptible. Though this is not always 

 practicable, it should be carried out whenever possible. The con- 

 version of pasturage into tillage is a good policy to adopt, but here 

 again the suggestion is not always feasible. Avoiding overstocking, 

 together with top dressing the land with salt, iron sulphate, or lime, 

 will do much to lessen the evil. 



Measures to be adopted against cestode infection of dogs and 

 cats have been discussed when considering bladder worms. 



DISTOMIASIS or FASCIOLIASIS. The trematodes of importance 

 to veterinary practitioners in this country are Fasciola hepatica 

 (Distomwn hepaticum) and F. lanceolata (the latter being less 

 common) of the horse, ox, sheep and goat. They are found in 

 the liver, stomach and intestines, in the pancreas and also in the 

 lungs and blood vessels, but before all others in the liver, causing 

 the disease known as " liver-rot." The life-cycle of F. hepatica is 

 as follows : The hermaphrodite flukes lay their eggs, of which 

 one may produce as many as 40,000, in the bile ducts of their host. 

 The eggs pass out with the faeces to the ground, and from these 

 3 to 6 weeks later there hatch out ciliated embryos which find their 

 way, if possible, to water in search of molluscs belonging to the 

 genus " Limnaeus." If the embryo succeeds in attaching itself 

 to a mollusc it penetrates its pulmonary cavity, where it develops 

 into a sporocyst. If no mollusc becomes available the life-cycle is 

 not completed and the embryo dies. The sporocyst may divide 

 into two or more sporocysts, from each of which arise six to eight 

 redid'. The latter then migrate to the liver of the mollusc, where 

 may be produced daughter redice. In the summer months each of 

 these may a second time produce daughter redicz. In the winter 

 months, however, development usually passes to the next stage, 

 which is that of the cercaria, about a score of which may be pro- 

 duced by each redia. The cercaria bores through the mollusc to 

 the outside, and being provided with a tail it propels itself and 

 becomes attached to a blade of grass, on which it becomes encysted. 

 If ingested by a sheep it undergoes slight changes and passes to 

 the bile ducts via the duodenum. Fillers gives the number of 

 adults which may develop from a single fluke at from nine to twelve 



