Animal Parasites. 73 



Into the bodies of these intermediary hosts the embryos of the round 

 worms find their way, and after passing a certain stage of their 

 existence there, they bore their way out again into the water, or perhaps 

 are swallowed along with their intermediary host by the animal in 

 which natTire intended them to become adult. Whether or not some 

 round worms can develop from the e^g stage to the adult form without 

 passing tlirough the body of an intermediary host does not necessitate 

 debate ; but the fact is incontrovertible that it is from water pools, 

 damp situations, and vegetable foods that animals, man included, 

 become infested with nematodes. Animals browsing over marshy 

 places, or drinking the water of pools in Avhich the ova were deposited, 

 pick up the embryos. Young children become infested from the filthy 

 practice of eating mud, and also by means of water drawn from impure 

 sources. Round worms abound all over the globe. They are denizens 

 of the torrid and frigid zones, and are al)undantly scattered over the 

 temperate regions. They are found in the lungs, liver, kidney, heart, 

 muscles, arteries, intestines, glands, eye, skin, &c., of their hosts. 



Lung Worms. 



Pastoralists and poultry-keepers are particularly interested in the 

 study of the life history and habits of lung worms. It is not uncommon 

 to find them in. the respiratory tracts of animals and birds, and 

 man even is not exempt. In the pig a lung worm is encountered, and 

 another is the cause of " hoose " in calves, exciting a hoarse bron- 

 chial cough and causing a difficulty in breathing. Imperfect aeration 

 of blood may occur from the blocking up of the air passages by the 

 worms, and this may bring about loss of condition in the calves. In 

 the trachea, or windpipe, of fowls a round worm, the Sclerosfoma 

 synyamus, is observed, which causes the disease known as " gapes." 

 The eggs from this worm escape from the mouths of the birds, and, if 

 they reach water, or are deposited on damp soils, they undergo a 

 certain stage of development. The embryos next bore their way into 

 the bodies of insects, snails, caterpillars, or molluscs, or perhaps bury 

 themselves in decaying vegetable matter or in the moist soils about 

 water pools. Fowls roaming ovei- damp places pick up the embryos 

 along with their food or water. The embryos find their way from the 

 mouth into the trachea, and there develop to the adult form. 



In the sheep, lung worm is particularly common, and may occasion 

 great mortality in lambs. The lung worm of the sheep is the Strongylus 

 jilaria. In the process of its development it. may pass through the 

 bodies of molluscs, snails or caterpillars, and then, after a time, it 

 may bore its way out to again enjoy a brief free existence. It only 

 flourishes in marshy or damp districts, and it is on such country that 

 young lambs, when grazing, pick up the embryos along with their 

 food or water. The embryos, on gaining the mouths of their hosts, 

 may find their way into the windpipe, and thence gain the ramifications 

 of the bronchial tubes. On reaching the lungs, the embryos develop 

 to adult form, and from the lungs the egg'S may escape with the secre- 



