PREVENTION OF VEEMICEOUS DISEASES. 507 



with the extract of male fern, about 10 drops administered in 

 salad-oil. 



Nematode or round-worms are little affected by the above, at 

 least the majority of species. The round-worms may or may not 

 have two distinct hosts. Such groups as the Trichinae live in two 

 different animals or in diiferent parts of the same animal. The 

 asexual forms live in the connective-tissue organs, and in the blood- 

 vessels, &c. ; the sexual forms in the intestines, the air-passages, 

 and a few beneath the skin. The majority of Nematodes pass their 

 eggs out in the host's dung, the worms coming away when their full 

 complement of eggs are laid. These ova lie about upon the ground, 

 get carried into the water, and are thus taken up again with food 

 and drink. Some undergo a slight development outside the host 

 upon the damp ground and vegetation ; and possibly some few may 

 live in a secondary host, such as earthworms, snails, insects, &c. 

 Some are carried by biting flies (Filarise and Mosquitoes). 



The well-known disease, trichinosis in pigs, rats, and men, is 

 distributed chiefly by rats, and through them it is given to pigs, 

 and from the latter to man. Here again the knowledge of the life- 

 history helps us, for by stopping the common practice of giving 

 dead rats to the pigs, we shall tend to check a disease which in 

 human beings may be attended with fatal results. The destruction 

 of rats is most necessary. 



Some pastures are known to be impregnated with certain 

 diseases, such, for instance, as lung-worm or husk, and the worms 

 producing parasitic gastritis. When this is known to be the case, 

 it is well to keep the animal subject to the disease off the land for 

 some time, feeding it down in the meanwhile with other stock 

 that are not invaded by the particular kind of parasite we wish 

 to destroy. In the red intestinal worms, the armed sclerostomes, 

 in horses, we can employ this way of clearing the paddocks by 

 grazing sheep on them for some time : these animals, feeding close 

 and making the land obnoxious by their excreta, destroy the 

 majority of the eggs passed out in the horses' dung, and are not 

 themselves invaded by the equine parasites. A large number of 

 round-worms live in the intestines of all animals, and as the ova 

 are passed out in the dung, it is very essential in an outbreak of 

 these nematodes to see that the diseased animals, such as horses, 

 are boxed and all the excrement burnt, whilst the meadows should 

 be kept free from the hosts, and if the disease is not an ovine one, 

 dressed with salt and fed down by sheep. Diseases, such as husk. 



