312 READINGS IN BIOLOGICAL SCIENCE 



for twenty-four hours and cut up with green peppers, cabbage and cu- 

 cumbers, while some bury the raw fish for a few days to ripen it, then eat 

 it with salt." 



At one time there was considerable discussion among parasitologists as 

 to whether the fish tapeworm could complete its life cycle in North Amer- 

 ica, some investigators taking the position that infested persons in this 

 country must have acquired this parasite abroad. It has been definitely 

 established, however, that the fish tapeworm has become endemic in North 

 America and many cases of infestation of native origin have been traced. 

 Fishes from the Great Lakes region of the United States have been found 

 to be naturally infested, and species of copepods that are capable of serving 

 as the first intermediate host have been shown to be susceptible to experi- 

 mental infection. Thus, the entire hfe cycle of this tapeworm can take 

 place in North America, and this parasite, originally introduced into this 

 country by immigrants from northern Europe, is now definitely established 

 in the United States. According to Ward the belt of infection stretches 

 across the Great Lakes, includes the upper Mississippi basin, even reaching 

 out into Iowa, crosses the height of land into Manitoba and embraces lakes 

 almost to the Rockies. 



Once having gained a foothold, it is easy to see how this parasite estab- 

 lished itself solidly, since untreated sewage from cities and towns is com- 

 monly emptied into lakes. Infested immigrants coming to North America 

 from countries along the shores of the Baltic and from other areas where 

 this infestation is common, polluted the lakes in some of our North Central 

 States and other regions. 



In parts of Scandinavia, Finland, Russia and Germany, bordering on 

 the Baltic and connecting waters, the local population shows an incidence 

 of infestation up to 50 per cent, or more. Even a few infested immigrants 

 could have greatly polluted our fresh-water lakes, since it has been esti- 

 mated that an infested person may discharge at least one million tapeworm 

 eggs a day. The fondness of certain people of European origin for raw fish 

 or portions thereof raw, or lightly salted or pickled, has served to propagate 

 this infestation in this country. The susceptibility of the dogs, cats and 

 various wild carnivores to this parasite has added a further complication 

 tending to increase the spread of this tapeworm. 



Persons infested with the fish tapeworm may exhibit nervousness, loss 

 of sleep, experience creeping feelings and occasionally show a voracious 

 appetite. The symptoms manifest themselves particularly after a person 

 discovers that he or she is infested, this indicating that the symptoms, at 

 least in part, are probably mental rather than physical. Of special interest 

 in connection with this parasite is the occurrence in a very*small percentage 

 of infested persons of an anemia that is indistinguishable from pernicious 

 anemia. However, precise information is still lacking with regard to the 



