AFFECTIONS OF THE INTESTINAL CANAL. 



about as thick as twine. The males are rare, about a line to a line 

 and a half long, and rolled up at the tail-end. The females are larger 

 and straight, or only slightly bent. The head of the thread-worm is 

 enlarged by wing-like attachments. The penis is at the tail-end of 

 the male. The sexual opening of the female is near the head. The 

 usual seat of this worm is the lower part of the intestine, particularly 

 the rectum, but they may even enter the lower part of the small intes- 

 tine. They often crawl out of the anus and enter the vagina, etc. 



The trichoceplialus dispar, the hair-headed or whip-worm, is about 

 an inch and a half or two inches long ; the posterior part is quite thick, 

 the anterior hair-like. In the male, which is the smaller, the posterior 

 part is wound into a spiral, and has at its end the hook-shaped penis 

 surrounded by a bell. The female is thicker and straight, and its pos- 

 terior end is full of eggs. The trichocephalus inhabits the large intes- 

 tine, particularly the ccecum. 



Development of Intestinal Worms, and Etiology of Helminthi- 

 asis. The time for believing in spontaneous generation, and in the 

 formation of intestinal worms by a collection and alteration of intes- 

 tinal mucus, has passed. The parasites living in the intestinal canal 

 originate from eggs, and have reached the intestines in that state, or 

 one further advanced. Of the tasnia solium and taenia mediocanellata 

 alone, we more accurately know the mode of development. The last 

 links (proglottides) of the tape-worm, which contain the ripe eggs, 

 occasionally drop off, and are evacuated. In order to develop further, 

 the embryos from the eggs must enter some other animal. If they are 

 swallowed by some animal, they pass from the intestines into the tissues 

 of the body, till they find a suitable place ; then they throw off the 

 little hooks, and a neck and head (scolex), resembling those of the 

 tape-worm, grow from their wall. At first the scolex is enclosed within 

 the embryo ; it subsequently becomes free, and the swollen body of 

 the embryo hangs to it like a bladder. At this stage of development 

 the scolices constitute the parasites known as cysticerci, or bladder- 

 worms ; the most common variety of them, those found in swine, called 

 cysticercus cellulosus, is the scolex of taenia solium. If this cysticercus 

 enters the intestines of a human being, it becomes attached to the 

 wall, drops the bladder-like tail, forms links, and becomes a tape-worm. 

 Taenia mediocanellata develops in the same way when a cysticercus 

 living in beef enters the intestines of man. The scolices of bothrio- 

 cephalus latus are unknown, as are also the first stages of ascaris lum- 

 bricoides, oxyuris vermicularis, and of trichocephalus dispar; but it is 

 certain that the young worms are not directly developed from the eggs 

 of worms existing in the intestines. Hence we must suspect that the 

 voung of these worms also are taken into the body with the food. 



