HISTOR Y—MTIOLOG Y 



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of the disease as seen in the Philippine Islands. In 1910 Nagano 

 reported upon the prevalence of the disease in Northern Formosa, 

 around the prefecture of Shinchika; and Nakagawa in 1913 and 

 1914 found 1,249 cases, of which 922 occurred in that prefecture, 

 and believes that there are not less than 13,000 cases therein. In 

 1912 Masuo and Yokokawa found the disease in Sansaka, Koryo, 

 Jukirin, and Nansho. In 1914 Nakagawa investigated the inhabi- 

 tants of the lowlands occupied by savage tribes, and found that 

 about 50 per cent, of the population were infected; but in the high- 

 lands the cases were less in number. 



In the meanwhile observations had been made as to the develop- 

 ment of the worm in the egg by Nakahama in Japan, by Manson in 

 China, and by Garrison and Leynes in the Philippines. In 1914 

 Nakagawa found that the cercariai developed in the moWnsc M elania 

 lihertina Gould, which lives in pools and sluggish streams; in 

 Melania obliquegranosa Smith, which inhabits slowly moving 

 streams; and in Melania tuberculata Mueller. 



The life-history would be as follows: — ^The miracidia attach them- 

 selves by means of suckers to the head, jaws, and feet of these 

 molluscs,and then bore their way by means of their proboscis into the 

 liver, the heart, and the kidneys, where they become sporocysts 

 and cercariae. These latter possess an unforked tail and measure 

 0*12 X 0*09 mm., and a tail of 0-054 They also show a spine, 



two suckers, three pairs of poison glands, and a heart-shaped excre- 

 tory vesicle. They encyst on the gills of certain crabs — viz., Potamon 

 {geothelphusa) obtusipes Stimpson, the red crab; Potamon {geothel- 

 phusa) dehaanii White, the dung crab; Eriocheir japonicus de Haan, 

 the hairy crab; and perhaps on those of Sesarma dehaanii Milne 

 Edwards, Sind Potamon {parathelphusa) sinensis Milne Edwards. 



Dogs fed upon these crabs showed eggs in ninety days after 

 infection. The young distome escapes from the cyst in the intestine 

 of the dog, pierces the wall of the jejunum and passes into the peri- 

 toneal cavity, pierces the diaphragm and pleura and enters the lungs, 

 where it encysts and becomes adult. 



More recently other observers have doubted the necessity of the 

 crab in the case of the infection of man, which apparently can take 

 place via the skin. 



Kobayashi believes that the cercariae observed by Nakagawa in 

 molluscs of the genus Melania are not those of P. ringeri. 



Climatology. — Paragonimiasis is found in China, Corea, Japan, 

 Formosa, the Philippine Islands, and Sumatra. The infection 

 is more prevalent among people living along large rivers, according 

 to Nakagawa, and less so among people who use well water. 



lEiiology. — -The causal agent is Paragonimus ringeri Cobbold 

 (p- 573) > which lives not merely in man, but also in the cat, the dog, 

 and the pig. The intermediate hosts are molluscs of the genus 

 Melania, in which the cercariae are developed, and these pass to 

 man either directly or through the agency of certain crabs, in which 

 they become encysted. Infection may be by the alimentary canal, 



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