PUESIDEXTIAL ADDRESS SECTION D. 83 



where a second redia is produced. Within this redia several 

 cercariae are formed, but one only matures, which may become 

 free-swimming. The free cercarise are 0-12 mm. long and 0-09 

 mm. wide. The tail is about 0-054 mm. long. The oral sucker 

 has two pear-shaped bodies attached to it. It also bears spines, 

 each with a ringlike border. The ventral sucker is much smaller 

 than tiie oral, being about 0-018 mm. in diameter. Three pairs 

 of mucin (or poison) glands are present, and there is a heart- 

 shaped excretory vesicle. When the free cercariae attack the 

 gills, muscles or liver of the crustacean host, or perhaps the snail 

 containing cercariae is devoured by a crustacean, the cercariae 

 encyst. The flesh of the Crustacea eaten in a raw or imperfectly 

 -cooked condition is the source of infection for mammals, including 

 man. 



The process of encystment and maturing talies about 30 days. 

 The encysted cercariae are long lived, and Kobayashi has found 

 that they can live as long as six years in crabs and then infect 

 experimental vertebrates. When the cysts reach the intestine of 

 the final host, the flukes emerge, pass through the intestine into 

 the abdominal cavity, wander towards the diaphragm, pierce it 

 and thus reach the pleural cavity and the lungs. Extensive 

 'dainage may be done during the migrations of the flukes, which 

 attain full maturity in the lungs. The early stages of human 

 infection are often considered the most harmful, the symptoms 

 resembling those of pneumonia. 



Vertebrate hosts of Paragoninius other than man are known. 

 Dogs, cats and pigs are known to be infected in Japan and 

 Formosa, as was shown by Nakagawa and by Kobayashi. Onji 

 (1921) has found the parasite in the faeces of weasels and 

 racoon dogs " in Japan. He believes that several other crab- 

 eating animals such as otters, bears, boars and monkeys are 

 probably also natviral hosts, and that ova passed with the faeces 

 •of these animals serve to infect the snails. He also thinks that 

 an additional source of human infection is by swallowing cysts 

 from dead crabs in drinking water. 



Paragonimus originally was confined to the Far East. Now 

 it has spread to South America, and particularly has increased 

 in Peru of recent 3'^ears, owing to the immigration especially of 

 Japanese and some Chinese sufferers, and the occurrence in Peru 

 of suitable invertebrate hosts. Tn 1910 the first case was demon- 

 strated in a Peruvian who had charge of a gang of Japanese 

 coolies, and the number of cases of Peruvians has increased 

 rapidly since then, the disease having become endemic. It has 

 also spread to North America. The occurrence of suitable native 

 Mollusca and Crustacea, as well as the importation of molluscs 

 from infected areas, coupled with the occurrence of a human 

 reservoir, may result in the introduction of such diseases as 

 paragonimiasis and clonorchiasis in any country. 



Metagonimiasis. 



Mctagoiiimus yokogaicai, Katsurada, 1913, is a small fluke 



-occurring in the adult condition in the upper and middle part of 



the jejunum of man, cat and dog, where they enter and destroy 



