THE ROUNDWORMS 



179 



7.- 



twelve inches. As a rule no serious 

 trouble is caused by them. The usual 

 symptoms are disordered digestion, 

 restlessness at night, and grinding of 

 the teeth. 



Trichina. — A very serious parasite 

 belonging to this group is the trichina 

 (Fig. 102), which causes the disease of 

 human beings, pigs, and rats called 

 trichinosis. The parasites enter the 

 human body through the eating of 

 inadequately cooked meat from an 

 infected pig. The larvae soon become 

 mature in the human intestine, and 

 each mature female deposits probably 

 about 10,000 young. These young 

 burrow through the intestinal wall and 

 encyst in the muscular tissue in vari- 

 ous parts of the body. As many as 

 15,000 encysted parasites have been 

 counted in a single gram of muscle. 



There is no remedy when one is 

 once parasitized by these worms, but 

 prevention is quite simple; never eat 

 pork that has not been thoroughly 

 cooked. Pigs acquire the disease by 

 eating offal or infested rats. 



Hookworm. — Another serious para- 

 site of man is the hookworm (Fig. 



Fig. ioi. — Anatomy of a female round- 

 worm, Ascaris. 



1, pharynx ; 2, intestine ; 3, ovary ; 4, uterus ; 

 5, vagina; 6, genital pore; 7, excretory tube; 

 8, excretory pore. (From Shipley and Mac- 

 Bride.) 



