A small, slender nematoid worm () which, in the larval state, is parasitic, often in immense numbers, in the voluntary muscles of man, the hog, and many other animals. When insufficiently cooked meat containing the larvae is swallowed by man, they are liberated and rapidly become adult, pair, and the ovoviviparous females produce in a short time large numbers of young which find their way into the muscles, either directly, or indirectly by means of the blood. Their presence in the muscles and the intestines in large numbers produces trichinosis.