150 THE FLATWORMS— PLATYHELMINTHES 



In order for the cycle to continue, a hog must eat these ripe proglot- 

 tids, and this frequently happens. Once in the intestine of the hog, the 

 shell of each egg is digested off and the little embryos, which now have 

 six hooks on their bodies, escape. They immediately burrow their way 

 into the intestinal wall and get into the blood stream through the little 

 capillaries which are so abundant in this region. They are then carried 

 over the body by the blood and leave the blood vessels when they reach 

 some of the muscles, which they bore into and encyst. Here they form 

 what is called a bladder worm which for many years was thought to be 

 an entirely separate animal. They are large enough to be seen with the 

 naked eye and are composed of an inverted scolex inside of a rounded 

 bladder. In this stage they live in a dormant condition throughout the 

 life of the hog. 



Photo by Winchester 



Fig. 10.10. Bladder worms of the pork tapeworm in a piece of infected pork. There 

 are eight worms visible in this piece of pork detected by meat inspectors at a slaughter 



house. 



Because they are rather easily spotted by trained meat inspectors, it 

 is very unusual for pork sold on the market to carry them. Thorough 

 cooking, of course, will kill them so there will be no infection, even 

 though they are present in the meat. However, it must be remembered 

 that, if fried very rapidly, a piece of pork sausage may be thoroughly 

 browned on the outside, yet the inside may be hardly warmed. It has 

 been shown that it takes a temperature of about 132 degrees to kill the 

 bladderworms. This does not seem very high when we consider that we 

 have air temperatures of 120 degrees and higher in some sections of our 

 country during the summer, yet a large piece of meat such as a ham, after 

 being boiled for two hours, may show a temperature of only 123 degrees 

 in its center. 



The beef tapeworm, Taenia saginata, has exactly the same life cycle ex- 

 cept that cattle are the intermediate host. These worms are extremely 



