256 FLAT WORMS 



INFECTIONS. 



Taenia saginata (Tsenia mediocanellata). This very widely dis- 

 tributed tape-worm is often termed the unarmed tape-worm, to dis- 

 tinguish it from the T. solium or armed tape-worm. 



It is from 10 to 25 feet long and has several hundred proglottides. The small 

 pear-shaped head has four pigmented elliptical suckers and no hooklets. The seg- 

 ments are plumper than those of T. solium, hence the name saginata. The single 

 lateral genital pore projects markedly and in a series of segments presents, as a rule, 

 first on one side, and then on the opposite side of the next segment (alternating). 

 The best way to distinguish a segment of the T. saginata from the T. solium is by 

 counting the number of lateral uterine branches; these number fifteen to thirty, are 

 quite delicate and branch dichotomously. The lateral divisions of the uterus of 

 the T. solium are tree-like in their branching and only number five to twelve on each 

 side. 



T. solium has three ovaries while T. saginata has only two. The ox is the inter- 

 mediate host. The eggs of Taenia have an oval outer shell which is filled with 

 rather translucent, refractile yolk, often in globules. Within the oval shell is the more 

 rounded cell of the six-hooked embryo with its thick striated membrane. The outer 

 shell is often absent in the eggs found in the faeces, only the shell of the six-hooked 

 embryo being found. The six-hooked embryo, having worked its way from the 

 alimentary canal to the muscles or liver of the ox, becomes encysted (Cysticercus 

 bovis). This little bladder-like structure is about 1/4 by 1/3 inches, and contains 

 but a small amount of fluid. Being ingested by man's eating raw or imperfectly 

 cooked meat, the adult stage becomes established in his alimentary canal. 



It is probable that the various raw-meat cures have made the infection more com- 

 mon. In Abyssinia the infection is said to be universal, and a man without a tape- 

 worm to be a freak. An important point is the fact that the larval stage almost 

 never appears in man. It is this fact which makes it a so much less dangerous para- 

 site than the T. solium, which readily establishes a larval existence in man if the ova 

 are introduced into the human stomach. Cooking meat always destroys the 

 cysticercus. A period of about two months elapses after the ingestion of the cysti- 

 cercus before the mature segments pass out of the rectum. These not only make 

 their exit with the faeces, but are also capable of wandering out at other times. In 

 this they differ from the segments of T. solium. T. saginata next to Hymenolepis 

 nana is the common tape-worm of the United States. Dr. Stiles has examined 

 several hundred tape-worms in the United States during the past few years and 

 has found only one T. solium. 



Abnormalities of the scolex and proglottides are not uncommon with T. saginata. 

 This is less frequently the case with T. solium. 



Tsenia solium. -The measly-pork tape-worm is smaller than the 

 T. saginata and differs from it in having a globular head, with a rostellum 

 which is crowned by twenty-six to twenty-eight hooklets. 



In T. saginata a depression takes the place of the armed rostellum; the suckers 



