102 ON ANIMAL PARASITES. 



Oxyuris, and the Ascaris. The Trichina spiralis is cystic in its 

 sexually immature condition in the muscles of the pig, and in 

 this state it is harmless, and incapable of further development 

 until a portion of the trichinatous pork be eaten by a warm- 

 blooded vertebrate, and so introduced into the alimentary canal, 

 when the immature worm escapes from its cyst, develops sexual 

 organs, and gives birth to nvmierous progeny. The young 

 TricJmim thus produced, perforate the walls of the alimentary 

 canal, and, working their way amongst the muscles, give rise to 

 the painful and A^ery often fatal disease known as trichinasis. 

 The young worms then become encysted, and cannot become 

 sexually mature or further developed until again transferred to 

 the alimentary canal of some other animaL The Guinea-worm 

 {Dracuncuhis or Filaria medcnensis) inhabits, during one stage of 

 its existence, the cellular tissue of the human body, generally 

 attacking the legs, where it remains embedded for a year or 

 more, after which it seeks the surface in order to breed. The 

 development of the young Filaria, takes place in water, from 

 whence it is believed to gain access to the ])ody of bathers and 

 others. The thread -worm (Strong i/his filaria) is the parasite 

 which occasions the " lamb disease, " by infesting the lungs of 

 the animal. The worm bores its way through the soft lung sub- 

 stance into the bronchial tubes, where it causes the irritation 

 symptomatic of the disease. The ova and young parasites are 

 supposed to be taken up with the food in the first instance, and 

 to gain access from the alimentary canal into the circulation, and 

 thence into the lung substance, where they are encysted, until 

 the parasite matures, when it pierces the tissues and enters the 

 bronchial tubes, causing the disease just mentioned. Many of 

 the worms remain encysted in the lungs unable to break through 

 the capsule, and the lungs of old sheep are often loaded Avith 

 them, but in the encysted forms they cause little inconvenience 

 to the host. The best means of prevention are to feed the lambs 

 on fresh, clean, and dry pastures, and when necessary supplement 

 the grcss with artificial food. Animals affected may be made to 

 inhale sulphurous gas, by burning sulphur, with the lambs con- 

 fined in a close building,. They should be supplied with plent}' 

 of stimulating food, and 10 to 20 grains of sulphate of iron ; each 

 lamb, besides, having free access to rock-salt. Another worm of 

 this class {Strongylus 7)iicrurus) produces the " husk " or " hoose " 

 in calves, which strongly resembles the " lamb disease." The 

 ova of this parasite is absorbed from the digestive system, the 

 parasite penetrating to the pulmonary tissue and bronchial tubes 

 through the circulation. The same worm has been found in the 

 air-passages of the horse and ass ; and a somewhat similar worm 

 {Strongylus suis) has been found in the pig. The " grouse disease " 

 is caused by Strongylus j)ergracilis, and " gapes " in fowls by 



