CHAPTER XXI 



NEMATODA. FAMILY V. STRONGYLID^. SUBFAMILY I. 

 METASTRONGYLINiE 



Worms of the Respiratory Tract 



Nematoda (p. 217). — The most prominent character by which this 

 family may be recognized is the caudal bursa of the male which is usually 

 well developed. The body is elongate, cylindrical, and in some cases 

 filiform. A buccal capsule may be present or absent and may be armed 

 with teeth in its interior. The esophagus is more or less enlarged poste- 

 riorly. The males have a more or less well-developed caudal bursa, 

 usually divided into lateral lobes, each supported by ray-Hke chitinous 

 thickenings. There are two equal or unequal spicules. The vulva of the 

 female may be posterior or anterior to the middle of the body, usually 

 posterior, in some cases near the anus. 



Parasitism. — While these worms in their adult form mostly infest 

 the lumen of the alimentary and respiratory tracts, other organs may be 

 primarily or secondarily involved. The subserous larval phase of in- 

 testinal invasion by the genus OEsophagostomum and the vascular 

 larvae of Strongylus vulgaris may be mentioned in this connection, while 

 other organs are not uncommonly invaded by migration. The term 

 strongylosis is a general one which has been applied to any helminthiasis 

 produced by strongyles. It is more precisely used when qualified by 

 terms indicating the seat of invasion, as gastric, intestinal, bronchial, 

 vascular, or renal strongylosis. 



Being responsible for some of the most depletive and fatal forms of 

 parasitism, the strongyl worms have especially demanded study and 

 investigation; this has established important advances in knowledge 

 as to their pathogenicity, though much remains to be revealed as to 

 their hfe histories and consequently as to effectual means for their 

 control. In general it may be said that low marshy pasturage and wet 

 seasons favor infestation with strongyles, which would indicate that the 

 ova and embryos of some forms at least are spread by water, and that 

 contaminated water and herbage are the vehicles by which the parasites 

 reach their hosts. 



As in other parasitic invasions, age and physical condition have a 

 decided influence in predisposition to strongylosis. Young ruminating 

 animals are especially susceptible to the broncho-pulmonary form, 

 while in all animals which may be affected both youth and senility favor 



