662 DISEASES OF SWINE 



power of selection the young parasite passes the entire length of the 

 small intestine, and does not stop and implant itself until it reaches 

 the commencement of the large intestine. Here it apparently finds 

 conditions suitable for its further growth and development, and it 

 attaches itself to the mucous membrane and becomes a perma- 

 nent inhabitant of this part of the bowel. 



Symptoms. — These parasites are relatively uncommon in the 

 United States, but are occasionally met with in the packing houses 

 and while making field postmortems. Even when present, the 

 whip-worms are usually in small number, and do not produce any 

 marked symptoms. In rare instances there may be enormous 

 numbers of the parasites in the bowel, and they then cause notice- 

 able disturbance. Loss of appetite, diarrhea, colicky pains, and 

 general unthriftiness, with loss of weight and aggressiveness, are the 

 usual symptoms. 



Treatment for these parasites is very much the same as that for 

 the simple round-worm. Prevention consists in keeping the ani- 

 mals on dry feed lots and feding on clean floors, so as to prevent 

 entrance of the ova or t^ggs into the stomach. Where the number 

 of worms in the bowel becomes large enough to produce serious 

 symptoms the hogs should be given a course of calomel and san- 

 tonin, or santonin and areca nut, following much the same direc- 

 tions as in the case of the treatment for Ascaris suilla. 



THORN-HEADED WORM (ECHINORHYNCHUS GIGAS) 

 This parasite is a very common one in the United States. It 

 is a worm which is found only in the hog, no other species of animal 

 harboring the parasite. The thorn-headed worm is so-called on 

 account of the fact that the biting apparatus of the head is armed 

 on either side with five or six spine-like thorns, by which the worm 

 is enabled to attach itself firmly to the lining membrane of the 

 bowel. It is often found in the small intestine of the hog, less 

 frequently also in the large bowel. The echinorhynchus is often 

 found in association with the common round-worm, but can be 

 easily distinguished from this parasite. While the round-worms 

 are often found in large numbers, it is unusual to find more than a 

 half-dozen of the thorn-headed worms in a single animal. 



Description. — The Echinorhynchus gigas is, as the name im- 



