278 THE ROUND WORMS 



8 inches (18 cm.) long and the female from 7 to 15 inches (30 cm.) in 

 length. They are from 1/7 to 1/4 of an inch (5 mm.) in diameter. 



It is probably the most common parasite of man, especially in 

 children and as it does not require an intermediate host infection takes 

 place through food or drink or by ringers of children who have been 

 playing where soil pollution exists. 



The normal habitat is the upper part of the small intestine, hence the ease with 

 which they are vomited up. The three papillae-like lips with a constriction just 

 behind are easily studied with a hand glass. The very long, whitish, convoluted, 

 thread-like tubes of the uterus lead to the- opening of the vulva anteriorly and ven- 

 trally. The male has two large lance-like spicules. 



The body of the worm is transversely striated and resembles the ordinary earth- 

 worm, but is more grayish than red. The ova are very characteristic with a rough 

 mammillated exterior. This at times is shelled off and we have a smooth egg which 

 may be mistaken for eggs of other parasites. The eggs leave the body in the faeces 



FIG. 77. Anterior extremity of Ascaris lumbricoides ; A, seen from front; B, seen 

 from dorsal surface. (Tyson after Railliet.) 



and after a long time a few weeks to several months, according to temperature 

 develop an embryo which remains in the shell until swallowed by man. It is stated 

 that they will remain alive for years. On being swallowed, the embryo leaves the 

 egg and we have males and females developing in the small intestine. In countries 

 where such parasites abound, as in Guam and the Philippines, the possibility of their 

 getting into the peritoneal cavity through operative measures on the intestine must 

 always be thought of. 



Guiart considers it probable that Ascaris may suck blood, produce intestinal 

 ulcerations and bacterial infections, and perforate intestine. Their entrance into 

 bile ducts or into larynx (vomited) must be considered. 



At autopsy they may be found perforating the appendix or even filling up the 

 pancreatic duct. 



Some think that the symptoms of itching of nose and anus, vertigo, or convul- 

 sions and anaemia may be due to a toxin secreted by the worm. 



Ascaris Canis. This is a parasite of the dog and cat, but is occasionally found 

 in children. It is much smaller than the A. lumbricoides male is 2 to 3 inches long, 



