II. NEMATHELMINTHES: NEMATODA 



267 



drink muddy water (Fellahin of Egypt) or work much with clay (pjotters and 

 brick-makers) are especially subject to infection. It was first known in Egypt; 

 caused considerable trouble during the building of the St. Gotthard tunnel in 

 Switzerland. More recently it has been recognized as frequent in our southern 

 states, where it has become notorious under the common names of hook-worm 

 and lazy worm. It has been thought that the Ankylostoma larva3 obtain 

 entrance to man through the skin, as in bathing, etc. 



Family 4. Trichotrachelid.e, These are called 'hair necks' because 

 that part of the body which contains the pharynx is hair-like and elongate. 

 Triclwcepliahis dispar* of man (fig. 248, A), about an inch or an inch and a half 

 in length, lives with its neck in the wall of the intestine near the ca;cum. Since 

 it does not move, it causes little injury. 



,4 C 



Fig. 248. — A, Trichocephalus dispar, male with anterior end embedded in intestinal 

 wall (from Leuckart). B, Trichina spiralis, male (from Hatschek). cl, cloaca; 

 t. testes. C, Trichina ia muscle (from Boas). 



Trichina spiralis* (fig. 248, B, C), is much smaller, but much more dangerous. 

 Two stages are to be distinguished, the encysted muscle Tricliina and the sex- 

 ually mature intestinal Trichina. The first was discovered in a human body 

 in 1S35; the latter was not known until much later. In the encysted stage it 

 occurs in the muscles of pigs, rats, mice, man, rabbits, guinea pigs, dogs, etc. 

 (never in birds) , enclosed in an oval capsule about o . 4 to o . 6 mm. long and hence 

 recognizable by a practised observer with the naked eye. Certainty in their 

 recognition demands a low power of the microscope. Coiled up in the capsule 

 is the worm, about i mm. long, which is not yet sexually mature. To attain 

 this it must be tran.sported into the intestine of another host. \\ hen, for instance, 

 man eats trichinosed pork the worms are freed by the digestive fluids and, enter- 

 ing the small intestine, become sexually mature in a few days. The female 

 (3-4 mm. long, the male 1.5 mm.) penetrates the intestinal villi and in course 

 of a month gives birth to 1500 (some say 10,000) living young, after which she 

 dies. The young enter the lymph vessels, are carried by way of the thoracic 

 duct into the blood-vessels, and wander into the muscles, especially those which 

 are much worked, like the diaphragm, eye muscles, and muscles of the neck, 

 and which consequently have a rich blood supply. They enter the sarcolemma 

 of the muscle, destroy the muscle substance, and finally become enclosed by a 

 capsule secreted by the host. The wandering takes place about the second 

 or third week after infection, the encystment in about three months. A slight 

 infection causes disagreeable symptoms; but where large numbers obtain 

 entrance the cases are frequently fatal. The worst epidemic known was in 



