THE ROUND WORMS AND FLAT WORMS 123 



invasion of the blood vessels and tissues that the worms 

 produce their greatest injury, and a great many deaths 

 have been caused by them. Infected pork may contain as 

 many as 80,000 encysted worms in a single ounce. As these 

 Trichina may produce many more young in the human 

 intestine a person may be infected with millions of these mi- 

 nute worms after eating raw pork. The Trichinae being 

 readily killed by heat, it is easy to avoid 

 these parasites by not eating pork that is 

 insufficiently cooked. One should be espe- 

 cially cautious about eating raw salt pork, 

 or raw smoked ham (both of which are 

 eaten by many people) because it has been 

 shown that the Trichinae are not killed 

 either by the salt brine or by the process- 

 of smoking. As in so many parasites the 

 Trichina requires two hosts, the eater and 

 the eaten, in order to complete its life 

 history. 



Another serious human parasite is the 

 hookworm of the southern states. The 

 young of this form live in damp earth and (From Leuck- 

 gain access to man by boring in through the 

 skin. People who went with bare feet in infected districts 

 often contracted what was known as " ground itch" 

 which is now known to be caused by the young hookworm. 

 When through the skin the worms are carried by the blood 

 throughout the body and many get into the alimentary 

 canal; here they grow to maturity and produce eggs which 

 are passed out of the body, where they hatch into 

 young worms. The latter live in the soil where they 

 await an opportunity to get into their host. When in 

 the human intestine the worms produce considerable dis- 

 turbance to general health, but they may be expelled 



