TRICHINELLA SPIRALIS 137 



diameter. The anus is terminal, the mouth is unarmed, 

 and the vaginal opening at the junction of the anterior 

 fifth with the rest of the body. There is only one ovary. 

 The males are smaller, about 1*5 mm. in length and 

 about 0*04 mm. in diameter. The cloaca is terminal and 

 lies between two caudal appendages. There are four 

 post-anal papillae but there is no spicule. 



Trichinella spiralis or Trichina spiralis (fig. 62) in its 

 sexual mature form maybe found in man, but ordinarily is 

 a parasite of rats or pigs. Many animals, both carnivora 

 and herbivora, may be artificially infected. In man infec- 

 tion is usually derived from pork, and the disease caused 

 is a serious one. 



The Trichina larvae encysted in the pork are still alive 

 when swallowed by man, unless they have been destroyed 

 in the process of cooking or otherwise preparing the 

 flesh of the pig for food. The larvae are set free in the 

 stomach and intestine. There they become active, and 

 in the duodenum and jejunum they become sexually 

 mature. The increase in size is not great, for the larvae 

 measure about 0*8 mm. in length, whilst when first 

 sexually mature they are only i'5 to r8 mm., and the 

 males ro to 1*2 mm. Copulation takes place in about 

 two days after the ingestion of the larvae, and the 

 males soon die, whilst the females continue to increase 

 in size, and in the course of a few days they nearly 

 double their length. They bore their way more or less 

 deeply into Lieberkuhn's glands, into the mucosa, and 

 ultimately into the lymphatic spaces. In these spaces 

 they pass their larvae, which at first are only 0*09 mm. in 

 length. They are carried mainly by the lymph and blood 

 to various parts of the body, but some appear to pass 

 through the tissues and into the peritoneal cavity. In 

 either case they ultimately come to rest in striated muscle. 

 These larvae reach their final destination in about nine 

 days after the infected pork has been ingested, but as 

 the female trichinella lives for five or seven weeks and 

 continues to pass larvae in numbers, the symptoms may 



