PARASITIC DISEASES 



169 



embryonic worms into the digestive tract along with 

 the food. Such conditions as favor the contamina- 

 tion of the food with the embryos, especially the 

 drinking-water, are the main predisposing causes. 

 Young and unthrifty hogs, because of their con- 

 dition, are predisposed to intestinal worms. Feeding 

 hogs on dirty feeding floors, or on the ground, and 

 drinking from ponds and dirty watering troughs, are 

 the common sources of infection. 



FIG. 20 — ROUND WORMS IN A PIECE OF INTESTINE 



Symptoms. — The symptoms are not characteristic 

 enough to enable us to diagnose this particular form 

 of intestinal parasitism, unless the worms are pres- 

 ent in the feces. The character of the symptoms 

 depend on the extent of the invasion. When only, a 

 few forms are present, but little disturbance in the 

 thriftiness of the animal is noted. But large num- 

 bers cause the lining membrane of the intestine to 



