CHAPTER XII 



TRICHINA, HOOKWORMS, FILARIA, AND OTHER 

 PARASITIC ROUND-WORMS 



The large group of hair-like or thread-like unseg- 

 mented worms, constituting the branch Nemathel- 

 minthes (Gr. nema, thread; helmins, worm), includes 

 certain kinds which on account of their parasitic 

 habits are of very great economic importance. Per- 

 haps the most familiar examples of the branch are 

 the hair-worms, or horse-hair snakes, which are often 

 found in watering troughs or pools of water. Be- 

 cause of their remarkable appearance many persons 

 believe them to be horse-hairs that have dropped 

 into water and changed into these animals. They 

 really come mostly from the bodies of insects in 

 which they pass a part of their lives as parasites. 

 The vinegar-eel, which is found in weak vinegar is 

 another common example of the group. 



Trichina. The dreaded trichina, Trichinella 

 spiralis, which causes the disease called trichinosis, 

 is a minute round- worm the adults of which live 

 in the intestine of man, pigs and other animals. 

 These adults produce living young which bore 

 through the walls of the intestine, and are carried 

 by the blood, or otherwise make their way to the 

 muscles, where they form little cells or cysts in 

 which they lie. The presence in the muscles of 

 thousands or millions of these little parasties often 

 causes great suffering, sometimes death to the host. 

 It has been estimated that the trichinosed flesh of 

 a human subject may contain 100,000,000 of these 

 encysted trichinae. Before further development of 



79 



FIG. 25. 

 vinegar-eel, 

 A n guillula 

 sp. (Great- 

 1 y magni- 

 fied; from 

 a living 

 specimen.) 



