766 PAEASITIG DISEASES. 



in cattle and slieep are not often spoken of as such, and little 

 attention is paid to those of the pig. With the cat, however, 

 it is far otherwise, for we have known veterinarians whose assis- 

 tance has been eagerly sought in view of ridding this domestic 

 pet of its internal enemies, and especially of the nematode 

 entozoon called Ascaris mystax. In addition to the above, there 

 are other species belonging to the nematode order, to which 

 a larger interest is, or ought to be, attached by the professional 

 man. To this series belong the little flesh-worm {Trichina 

 spiralis) ; the thread-worm which occasions the " lamb disease " 

 {Strongyliis Jilaria) ; the very similar nematode that produces 

 husk or hoose in cattle {Strongyhis micrurus) ; and the worm 

 which gives rise to aneurisms in the horse and ass (Strongyhis 

 armatus). No member of the veterinary profession should be 

 totally unacquainted with the natural history of these important 

 species of parasite. 



Except as regards the Tricliina spiralis, it cannot be affirmed 

 that we have an entire knowledge of the course of development 

 undergone by any of the above-mentioned nematodes. It is 

 true that, with more or less deviation from a common plan, all 

 of them must pass through similar stages of growth, from the 

 time of their first formation in the egg up to the period of sexual 

 maturity. All, moreover, must in some way or other conform 

 to a known law of their existence, which involves at least one 

 change of residence before tliey can acquire the adult condition 

 within the body of the last or ultimate bearer. Herein lies the 

 difficulty in tracing out the development of most of the species ; 

 nevertheless, from the facts already made known by experimental 

 research, it is not too much to hope that we shall hereafter become 

 possessed of a knowledge of all the more important phenomena 

 connected with the development of tlie nematode worms. 



The Trichina spiralis, as ordinarily known, is a small sexually 

 immature nematode, usually found lodged within capsules or 

 cysts, and occupying the muscles of some animal, such as the 

 pig, or of man himself. When tlie little worm is removed from 

 the cyst its entire length will be found not to exceed the -^^^h. of 

 an inch. In its full-grown or sexually mature state it is still a 

 very minute worm ; the males measuring only the iV^h of an 

 inch, whilst the females, which are more than as large again, 

 reach up to about -|^th of an inch. 



