676 



NEMA THELMTNTHES 



Triehinella spiralis Owen, 1835, 

 Synonym. — Trichina spiralis Owen, 1835. 



T. spiralis, though discovered by Paget in 1835 and described by Owen, 

 had been previously seen by Peacock in 1828 and by Hilton in 1833. 



It is really a parasite of the black rat [Epimys rattus) and the sewer rat 

 [E. norvegicus), in which the rate of infection is placed from 8*3 to 100 per 

 cent., according to the locality, but it spreads from the rat to pigs, dogs, 

 cats, and many other animals. 



Man becomes infected from the pig as a rule, for that animal is particularly 

 liable to the disease, because it is apt to be fed upon scraps of raw meat. 

 Further, the larva in the flesh of the pig is very difficult to kill, for it, will 

 resist a temperature of 80° C, pickling, smoking, and freezing. Hence, though 

 ham be well boiled, it does not follow that the larvae in its centre are killed. 

 Sausages, however, are the greatest danger, for in them the larvae can live well 

 protected. 



In order to infect man, there must be a source of infection for the pig, 

 and this, in the first instance, can come from the rat, and afterwards be kept 

 up in the pig, and then the transmission to man is easy. 



As rats, pigs, and men are cosmopolitan, so trichiniasis is also cosmopolitan. 

 It is not uncommon in certain parts of India, and is known in China. In 

 considering the endemicity of the disease, it must not be forgotten that the 

 wild boar {Sus scrofa ferox) is susceptible. The disease is supposed to have 

 been introduced into Europe from Asia, either by Epimys norv&gicus at the 

 end of the eighteenth century, or by the Chinese pig from 1820 to 1830. At 

 present it is common also in America. 



Morphology and Life-History. — It is usually found in human or pig's 

 muscles, where it appears as minute white specks, which, when magnified, 

 are found to be encysted larvae. These cysts are oval, with their long axis 

 in the same direction as that of the muscular fibres, measuring 400 by 250^. 

 The cyst membrane is formed from inflamed connective tissne, whi<j}i has 

 invaded the infected muscular fibre. Inside the cyst is the coiled-up worm. 

 In this condition the larvae may live for years, but may be killed by calcifica- 

 tion. They are mostly found in the diaphragm, the larynx, tonguf, abdo- 

 minal and intercostal muscles. 



When these cysts reach the stomach of a man or animal, the gastric juice 

 dissolves the cyst-wall, and the parasites escape, and, entering the duodenum 

 and jejunum, they grow into adult males 3 to 4 millimetres long by 60 jbi in 

 diameter, and females i'4 to i'6 millimetres long by 40 /j, in diameter, which 

 copulate. The males now die off, and the females, increasing in size, penetrate 

 the mucosa of the bowel until they reach a lymph-channel, where they de- 

 posit their larvae, which are born alive. Leuckart says one female gives rise 

 to 1,500 larvae, which are carried by the lymph and blood streams all over the 

 body. The larvae now leave the capillaries and work th^ir way into the 

 tissues, and in about nine to ten days encapsule in the muscles, the attacked 

 fibres of which degenerate and become inflamed, and the cyst already described 

 is formed. 



Pathogenicity.— When the female pierces the mucosa, and during the wan- 

 dering through the lymph and blood of the larvae, very severe symptoms 

 called trichinosis or trichiniasis are produced. 



Subfamily TRicHURiNiE Ransom, 1911. 

 Type GenvLS,—Trichuris ; also Capillaria Zeder, 180Q. 



Trichuris Roederer and Wagler, 1761 . 

 Trichosomidae, with the anterior part of the body very long 

 and thread-like, and the posterior thicker portion sharply trun- 



